Add RMPOPT support.

From: Ashish Kalra <[email protected]>

In the SEV-SNP architecture, hypervisor and non-SNP guests are subject to RMP checks on writes to provide integrity of SEV-SNP guest memory.

The RMPOPT architecture enables optimizations whereby the RMP checks can be skipped if 1GB regions of memory are known to not contain any SNP guest memory.

RMPOPT is a new instruction designed to minimize the performance overhead of RMP checks for the hypervisor and non-SNP guests.

RMPOPT instruction currently supports two functions. In case of the verify and report status function the CPU will read the RMP contents, verify the entire 1GB region starting at the provided SPA is HV-owned. For the entire 1GB region it checks that all RMP entries in this region are HV-owned (i.e, not in assigned state) and then accordingly updates the RMPOPT table to indicate if optimization has been enabled and provide indication to software if the optimization was successful.

In case of report status function, the CPU returns the optimization status for the 1GB region.

The RMPOPT table is managed by a combination of software and hardware. Software uses the RMPOPT instruction to set bits in the table, indicating that regions of memory are entirely HV-owned. Hardware automatically clears bits in the RMPOPT table when RMP contents are changed during RMPUPDATE instruction.

For more information on the RMPOPT instruction, see the AMD64 RMPOPT technical documentation.

As SNP is enabled by default the hypervisor and non-SNP guests are subject to RMP write checks to provide integrity of SNP guest memory.

This patch-series adds support to enable RMP optimizations for up to 2TB of system RAM across the system and allow RMPUPDATE to disable those optimizations as SNP guests are launched.

Support for RAM larger than 2 TB will be added in follow-on series.

This series also adds support to disable CPU hotplug while SNP is active, as the SEV firmware enumerates CPUs at SNP initialization and is not aware of the OS bringing CPUs online or offline afterwards. This also keeps the set of CPUs stable for the asynchronous RMPOPT scan, so the per-core RMPOPT_BASE MSRs programmed during setup remain valid.

This series also introduces support to re-enable RMP optimizations during SNP guest termination, after guest pages have been converted back to shared.

RMP optimizations are performed asynchronously by queuing work on a dedicated workqueue after a 10 second delay.

Delaying work allows batching of multiple SNP guest terminations.

Once 1GB hugetlb guest_memfd support is merged, support for re-enabling RMPOPT optimizations during 1GB page cleanup will be added in follow-on series.

v14:
- 3/5 (Initialize RMPOPT MSRs): remove rmpopt_disable() and the RMPOPT_BASE teardown from this patch. RMPOPT is now set up once and not torn down, so the RMPOPT_BASE MSRs are left in place on shutdown; the (now minimal) disable path moves to 4/5.
- 4/5 (async RMPOPT): rework the setup/teardown -- initialize once and do not tear it down. rmpopt_disable() now only cancels the pending re-optimization pass. Use a dedicated per-CPU workqueue (WQ_PERCPU) and drop the migrate_disable()/migrate_enable() around the local warm-up scan. Add a binutils-version comment above the RMPOPT .byte encoding and trim redundant comments and the 2 TB pr_info(). Reword the subject to "Perform RMP optimizations asynchronously".
- 5/5 (Re-enable on guest shutdown): move the call-site comment onto the snp_rmpopt_all_physmem() definition and simplify the RMPOPT_WORK_TIMEOUT comment.
- Correct the Suggested-by/Reviewed-by tags across the series.

Review feedback from Borislav Petkov.

v13:
- 3/5 (Initialize RMPOPT MSRs): use cpu_primary_thread_mask directly instead of building a local rmpopt_cpumask -- all primary threads are online while SNP is active, so the two are equivalent. Rename snp_cleanup_rmpopt() to rmpopt_disable().
- 4/5 (async RMPOPT): drop the leader/follower bookkeeping. Warm the RMP scan cache once, then fan the RMPOPT out to cpu_primary_thread_mask; re-running RMPOPT on the warm-up CPU is a cache hit, so the separate follower cpumask and the cpumask_andnot() are no longer needed. Rename rmpopt_work_handler() to do_rmpopt_work() and drop the now-unused this_cpu.
- Add Reviewed-by: Tom Lendacky <[email protected]> to the series.

Review feedback from Borislav Petkov.

v12:
- Merged the former "Add interface to re-enable RMP optimizations" and "KVM: SEV: Perform RMP optimizations on SNP guest shutdown" patches into a single patch (now 5/5), since the interface has no user without the KVM caller. The series is now 5 patches.
- 2/5 (Disable CPU hotplug): drop a stray reference to later patches from the commit message and trim the snp_prepare() comment. Move cpu_hotplug_enable() to the end of snp_shutdown(), after clear_rmp() and the mfd_reconfigure() IPI, so no all-CPU operation runs after hotplug is re-enabled.
- 3/5 (Initialize RMPOPT MSRs): restructure snp_probe_rmptable_info() so the contiguous probe (which clears X86_FEATURE_RMPOPT) is the common fall-through, also covering X86_FEATURE_SEGMENTED_RMP advertised but disabled by firmware. Move snp_setup_rmpopt() to the end of __sev_snp_init_locked(). Give snp_cleanup_rmpopt() its own short comment in snp_shutdown().
- 4/5 (async RMPOPT): document the optimization trigger points in the commit message. Rename enum rmpopt_function to rmpopt_op_type. Merge __rmpopt() into rmpopt() and replace rmpopt_smp() with a new rmpopt_scan_range() that loops as the on_each_cpu() callback, so the follower scan issues one IPI per core rather than one per 1GB. Use u64 for physical addresses. Allocate the follower cpumask once at setup. Document rmpopt_wq as the setup sentinel. Move the RMPOPT_WORK_TIMEOUT define to the guest-shutdown patch (its only user) as (10 * MSEC_PER_SEC). Remove a spammy pr_info() and reword comments.
- 5/5 (Re-enable RMP optimizations on SNP guest shutdown): document why re-optimization is driven by guest teardown (the only event that returns guest memory to hypervisor ownership); reword the commit message (s/clear/disable/ for optimizations, drop "Conversely").

Review feedback from Borislav Petkov.

v11:
- Reordered so "Disable CPU hotplug while SNP is active" (2/6) precedes "Initialize RMPOPT configuration MSRs" (3/6): the RMPOPT setup/cleanup code is then introduced with CPU hotplug already disabled and never takes cpus_read_lock().
- 1/6 (cpufeatures): drop the tools/arch/x86/include/asm/cpufeatures.h change and adopt the commit message as applied by Boris.
- 2/6 (Disable CPU hotplug): reword the commit message. Drop the redundant cpus_read_lock()/cpus_read_unlock() in snp_prepare() in this same patch -- with hotplug disabled the online CPU mask is stable, so the read lock is not needed and hotplug handling has no hole when bisecting.
- 3/6 (Initialize RMPOPT MSRs): replace the rmpopt_capable bool with a small helper local to arch/x86/virt/svm/sev.c -- cpu_feature_enabled(X86_FEATURE_RMPOPT) && cc_platform_has(CC_ATTR_HOST_SEV_SNP) -- clearing X86_FEATURE_RMPOPT for a contiguous (non-segmented) RMP in snp_probe_rmptable_info() (runs at BSP init, before alternatives). Rename rmpopt_cleanup() to snp_cleanup_rmpopt() to match snp_setup_rmpopt(). Both are introduced without cpus_read_lock() (hotplug is already disabled by 2/6). Simplify the RMPOPT_BASE comments. Drop the now-unused <asm/sev.h> include from core.c.
- 4/6 (async RMPOPT): the follower scan is likewise introduced without cpus_read_lock(). Drop the cond_resched() calls (nops on x86). On re-initialization after a legacy SNP shutdown, re-queue the optimization pass instead of skipping it. pr_warn() on cpumask allocation failure.

Review feedback from Borislav Petkov and K Prateek Nayak.

v10:
- Rework the CPU-hotplug patch (3/6): disable CPU hotplug in snp_prepare(), before SnpEn is set, instead of late in __sev_snp_init_locked(), so no CPU can come online without SnpEn during SNP initialization (per upstream review). Tie hotplug to SnpEn: it stays disabled while SnpEn is set -- including across a failed SNP_INIT and across the legacy SNP_SHUTDOWN_EX path -- and is re-enabled only once the firmware clears SnpEn on the x86_snp_shutdown path. Drop the separate idempotent flag: snp_prepare() re-enables hotplug on its own early failure, and a kexec target that boots with SnpEn already set disables hotplug once in snp_rmptable_init(). Reword the commit log and comments accordingly.
- Emit a pr_warn() in rmpopt_work_handler() (4/6) when the follower cpumask allocation fails, instead of silently skipping the optimization pass.

Sashiko AI upstream review identified several of the above issues.

v9:
- Rename rmpopt_configured to rmpopt_capable.
- Make rmpopt_cpumask a cpumask_var_t (allocated/freed at setup/cleanup) instead of a static cpumask_t.
- Drop the v8 WARN_ON_ONCE() on the RMPOPT_BASE writes; use a plain wrmsrq_on_cpu(), matching the SNP MSR-write convention in this file.
- Disable CPU hotplug with cpu_hotplug_disable()/cpu_hotplug_enable() (per tglx); re-enable only on the full x86_snp_shutdown path.
- Simplify rmpopt_work_handler() to a single leader-then-followers path:
with CPU hotplug disabled while SNP is active and snp_prepare() requiring all CPUs online when RMPOPT_BASE is programmed, every core is always programmed, so the explicit-leader fallback is now unreachable. Drop it along with the v8 work_on_cpu()/rmpopt_leader_fn() helper.
- Drop the debugfs interface (was patch 7/7) and its report-only plumbing; observability will be revisited after this series is merged.
- Restrict snp_rmpopt_all_physmem()'s export to the kvm-amd module.
- Use scoped_guard(cpus_read_lock) for the per-CPU MSR and follower loops.

Sashiko AI upstream review identified several of the above issues.

v8:
- Add a new patch to disable CPU hotplug while SNP is active, keeping the CPU set stable for the RMPOPT work handler.
- Drop the setup_clear_cpu_cap(X86_FEATURE_RMPOPT) calls; the rmpopt_configured bool is the runtime guard.
- WARN_ON_ONCE() on the RMPOPT_BASE MSR writes that previously ignored their return value.
- Simplify rmpopt_work_handler() by removing the explicit-leader
fallback: with CPU hotplug disabled while SNP is active and snp_prepare() requiring all CPUs online when RMPOPT_BASE is programmed, every core is always programmed, so the running CPU can always be the leader. This drops the smp_call_function_single() fallback (and with it the AB-BA deadlock and IRQ-latency concerns) and collapses the leader selection into a single leader-then-followers path.
- Use mod_delayed_work() in snp_rmpopt_all_physmem() so the batching delay tracks the last SNP guest termination.

Sashiko AI code review identified several of the above issues.

v7:
- Sync tools/arch/x86/include/asm/cpufeatures.h to mirror the kernel header for X86_FEATURE_RMPOPT.
- Fix commit title to use X86_FEATURE_RMPOPT to match the code (was X86_FEATURE_AMD_RMPOPT).
- Add static bool rmpopt_configured, set only when segmented RMP setup succeeds in setup_rmptable(). Check rmpopt_configured alongside cpu_feature_enabled(X86_FEATURE_RMPOPT) in snp_setup_rmpopt() and snp_rmpopt_all_physmem(), because setup_clear_cpu_cap() is unreliable after alternatives are patched. Add snp_clear_rmpopt_configured() called from amd_cc_platform_clear() when CC_ATTR_HOST_SEV_SNP is cleared. Do not use __ro_after_init on rmpopt_configured since the writer snp_clear_rmpopt_configured() is not __init.
- Add cond_resched() to all three leader loops in rmpopt_work_handler() to prevent soft lockups on systems with up to 2TB of RAM.
- Add comment above __rmpopt() documenting the RMPOPT instruction encoding (F2 0F 01 FC) and register interface (RAX = system physical address input, RCX = operation type input, RFLAGS.CF = output).
Note: RMPOPT does not modify RAX unlike PVALIDATE/RMPUPDATE, so the existing "a" (input-only) constraint is correct.

Sashiko AI code review identified several of the above issues.

v6:
- Drop wrmsrq_on_cpus() helper; use for_each_cpu() with wrmsrq_on_cpu() instead, as RMPOPT_BASE MSR programming is not performance-critical.
- Rewrite rmpopt_work_handler() leader selection to use a local follower_mask copy instead of modifying the global rmpopt_cpumask. This eliminates the current_cpu_cleared tracking and the restore at the end, and removes the need for synchronization comments about transient cpumask inconsistency.
- Add three-way leader selection in rmpopt_work_handler():
1. Current CPU is a primary thread in cpumask: run leader locally.
2. Current CPU is a sibling thread whose primary is in cpumask:
run leader locally (RMPOPT_BASE MSR is per-core), remove the primary from followers via cpumask_andnot(topology_sibling_cpumask).
3. Current CPU's core has no RMPOPT_BASE MSR programmed: pick an explicit leader via cpumask_first() + smp_call_function_single() to avoid #UD, with cpus_read_lock() around the IPI loop.
- Add WARN_ON_ONCE guard for empty cpumask in the explicit leader fallback path, with migrate_enable() before goto out.
- Add .llseek = seq_lseek to rmpopt_table_fops for consistency with other seq_file-based debugfs files and to support tools like "less".
- Change debugfs file permissions from 0444 to 0400 to restrict access to root only.
- Add comment in rmpopt_table_seq_show() explaining why cpu_online_mask is safe: RMPOPT_BASE MSR is per-core and snp_prepare() ensures all CPUs are online when the MSR is programmed.

Sashiko AI code review identified several of the above issues.

v5:
- Introduce rmpopt_cleanup() to tear down workqueue, debugfs, cpumask, and MSR state, called from snp_shutdown().
- Introduce rmpopt_wq_mutex to serialize snp_setup_rmpopt(), snp_rmpopt_all_physmem(), and rmpopt_cleanup().
- Introduce rmpopt_show_mutex to serialize debugfs reporting of rmpopt_report_cpumask.
- Move snp_rmpopt_all_physmem() call after SNP DECOMMISSION during guest shutdown.
- Use migrate_disable()/migrate_enable() for CPU pinning in the rmpopt_work_handler() leader loop to maintain CPU affinity without disabling preemption for the entire RMPOPT scan.
- Add cpus_read_lock()/cpus_read_unlock() around the follower on_each_cpu_mask() loop in rmpopt_work_handler().
- Guard snp_setup_rmpopt() against re-initialization when SNP_SHUTDOWN_EX with x86_snp_shutdown=0 skips rmpopt_cleanup() but clears snp_initialized, preventing workqueue and resource leaks on repeated init/shutdown cycles.
- Replace setup_clear_cpu_cap() with pr_err() on alloc_workqueue() failure in snp_setup_rmpopt(), as setup_clear_cpu_cap() cannot be used after alternatives are patched; callers check rmpopt_wq != NULL as the runtime guard instead.
- Add pr_info() when RMPOPT coverage is capped at 2TB.
- Add comments noting CPU hotplug is not supported with SNP enabled and only online primary threads are covered by rmpopt_cpumask.
- Add comment in setup_rmptable() noting Segmented RMP must be enabled to enable RMPOPT.
- Simplify cpumask setup loop to set if primary thread rather than skip if not primary.
- Improve grammar and clarity in snp_setup_rmpopt() comments.
- Added Reviewed-by's.

Sashiko AI code review identified several of the above issues.

v4:
- Add new wrmsrq_on_cpus() helper to write same u64 value to a per-CPU MSR across a cpumask without per-cpu struct allocation overhead.
- Rename configure_and_enable_rmpopt() to snp_setup_rmpopt().
- Use wrmsrq_on_cpus() instead of wrmsrq_on_cpu() loop for programming RMPOPT_BASE MSRs.
- Add setup_clear_cpu_cap(X86_FEATURE_RMPOPT) if segmented RMP setup fails or workqueue allocation fails.
- Add X86_FEATURE_RMPOPT feature clear logic in amd_cc_platform_clear() for CC_ATTR_HOST_SEV_SNP.
- All of the above allow checking for only X86_FEATURE_RMPOPT for both RMPOPT setup/enable and RMP re-optimizations.
- Rename snp_perform_rmp_optimization() to snp_rmpopt_all_physmem().
- Split rmpopt() into rmpopt() and rmpopt_smp() for SMP callback use.
- Introduce separate rmpopt_report_cpumask for debugfs reporting, distinct from rmpopt_cpumask used for primary thread tracking.
- Remove snp_perform_rmp_optimization() call from __sev_snp_init_locked() and instead setup and enable RMPOPT after SNP is enabled and initialized.

v3:
- Drop all RMPOPT kthread support and introduce adding custom and dedicated workqueue to schedule delayed and asynchronous RMPOPT work.
- Drop the guest_memfd inode cleanup interface and add support to re-enable RMP optimizations during guest shutdown using the asynchronous and delayed workqueue interface.
- Introduce new __rmpopt() helper and rmpopt() and rmpopt_report_status() wrappers on top which use rax and rcx parameters to closely match RMPOPT specs.
- Use new optimized RMPOPT loop to issue RMPOPT instructions on all system RAM upto 2TB and all CPUs, by optimizing each range on one CPU first, then let other CPUs execute RMPOPT in parallel so they can skip most work as the range has already been optimized.
- Also add support for running the optimized RMPOPT loop only on one thread per core.
- Replace all PUD_SIZE references with SZ_1G to conform to 1GB regions as specified by RMPOPT specifications and not be dependent on PUD_SIZE which makes the RMPOPT patch-set independent of x86 page table sizes.
- Use wrmsrq_on_cpu() to program the RMPOPT_BASE MSR registers on all CPUs that removes all ugly casting to use on_each_cpu_mask().
- Fix inline commits and patch commit messages

v2:
- Drop all NUMA and Socket configuration and enablement support and enable RMPOPT support for up to 2TB of system RAM.
- Drop get_cpumask_of_primary_threads() and enable per-core RMPOPT base MSRs and issue RMPOPT instruction on all CPUs.
- Drop the configfs interface to manually re-enable RMP optimizations.
- Add new guest_memfd cleanup interface to automatically re-enable RMP optimizations during guest shutdown.
- Include references to the public RMPOPT documentation.
- Move debugfs directory for RMPOPT under architecuture specific parent directory.

Ashish Kalra (5):
x86/cpufeatures: Add X86_FEATURE_RMPOPT feature flag x86/sev: Disable CPU hotplug while SNP is active x86/sev: Initialize RMPOPT configuration MSRs x86/sev: Perform RMP optimizations asynchronously x86/sev: Re-enable RMP optimizations on SNP guest shutdown

 arch/x86/include/asm/cpufeatures.h |   2 +-
 arch/x86/include/asm/msr-index.h   |   3 +
 arch/x86/include/asm/sev.h         |   4 +
 arch/x86/kernel/cpu/scattered.c    |   1 +
 arch/x86/kvm/svm/sev.c             |   2 +
 arch/x86/virt/svm/sev.c            | 201 +++++++++++++++++++++++++++--
 drivers/crypto/ccp/sev-dev.c       |   2 +
 7 files changed, 200 insertions(+), 15 deletions(-)

2.43.0

From: Ashish Kalra <[email protected]>

Add a flag indicating whether RMPOPT instruction is supported.

RMPOPT is a new instruction that reduces the performance overhead of RMP checks for the hypervisor and non-SNP guests by allowing those checks to be skipped when 1-GB memory regions are known to contain no SEV-SNP guest memory.

For more information on the RMPOPT instruction, see the AMD64 RMPOPT technical documentation.

[ bp: Zap respective tools/ change. ]

---
 arch/x86/include/asm/cpufeatures.h | 2 +-
 arch/x86/kernel/cpu/scattered.c    | 1 +
 2 files changed, 2 insertions(+), 1 deletion(-)

index f70ee74b5f92..3b5b32d3391b 100644
@@ -76,7 +76,7 @@
 #define X86_FEATURE_K8			( 3*32+ 4) /* Opteron, Athlon64 */
 #define X86_FEATURE_ZEN5		( 3*32+ 5) /* CPU based on Zen5 microarchitecture */
 #define X86_FEATURE_ZEN6		( 3*32+ 6) /* CPU based on Zen6 microarchitecture */
-/* Free                                 ( 3*32+ 7) */
+#define X86_FEATURE_RMPOPT		( 3*32+ 7) /* Support for AMD RMPOPT instruction */
 #define X86_FEATURE_CONSTANT_TSC	( 3*32+ 8) /* "constant_tsc" TSC ticks at a constant rate */
 /* free: was #define X86_FEATURE_UP	( 3*32+ 9) * "up" SMP kernel running on UP */
 #define X86_FEATURE_ART			( 3*32+10) /* "art" Always running timer (ART) */

index 8665a6474806..d1795ce219da 100644
@@ -67,6 +67,7 @@ static const struct cpuid_bit cpuid_bits[] = {
 	{ X86_FEATURE_PERFMON_V2,		CPUID_EAX,  0, 0x80000022, 0 },
 	{ X86_FEATURE_AMD_LBR_V2,		CPUID_EAX,  1, 0x80000022, 0 },
 	{ X86_FEATURE_AMD_LBR_PMC_FREEZE,	CPUID_EAX,  2, 0x80000022, 0 },
+	{ X86_FEATURE_RMPOPT,			CPUID_EDX,  0, 0x80000025, 0 },
 	{ X86_FEATURE_AMD_HTR_CORES,		CPUID_EAX, 30, 0x80000026, 0 },
 	{ 0, 0, 0, 0, 0 }
 };

2.43.0

From: Ashish Kalra <[email protected]>

While SNP is active, every memory write is checked against the RMP to protect SNP guest memory. A core performs these RMP checks only once SNP has been initialized via SNP_INIT and the SNP-enable bit in SYSCFG is set on that core; the firmware requires the SNP-enable bit to be set on every present CPU before SNP initialization.

A core that is not SNP-enabled and not SNP-initialized performs no RMP checks at all, so there is no valid configuration with SNP active and any CPU exempt from RMP checks.

The firmware determines which CPUs are present from the processor and the BIOS/UEFI configuration (e.g. SMT disabled in the BIOS) and enumerates them at SNP init; it is not aware of the OS bringing CPUs online or offline afterwards.

SNP_INIT fails unless SnpEn is set on all CPUs, so a CPU that is offline when SNP_INIT is issued, does not have SnpEn set, SNP_INIT fails, and there can be no SNP guest memory. OS CPU hotplug can thus diverge from the firmware's expectations and break SNP.

Tie CPU hotplug to the SNP-enable bit: disable it in snp_prepare() before SNP is enabled, and re-enable it in snp_shutdown() once the firmware has disabled SNP.

If snp_prepare() fails before enabling SNP it re-enables hotplug itself; once SNP is enabled hotplug stays disabled, including across a failed SNP_INIT and across the legacy SNP_SHUTDOWN_EX path, both of which leave SNP enabled.

A kexec target that boots with SNP already enabled, disables hotplug once in snp_rmptable_init(), since snp_prepare() bails when SNP is already enabled.

With CPU hotplug now disabled while SNP is active, the online CPU mask is stable, so the cpus_read_lock() previously taken in snp_prepare() to iterate it is redundant. Drop cpus_read_lock()/cpus_read_unlock() here.

---
 arch/x86/virt/svm/sev.c | 36 ++++++++++++++++++++++++++----------
 1 file changed, 26 insertions(+), 10 deletions(-)

index cff285d8ad8e..558f7924a3f8 100644
@@ -513,7 +513,6 @@ static void clear_hsave_pa(void *arg)
 
 int snp_prepare(void)
 {
-	int ret;
 	u64 val;
 
 	/*

@@ -526,14 +525,18 @@ int snp_prepare(void)
 
 	clear_rmp();
 
-	cpus_read_lock();
+	/*
+	 * No CPU may come online without SnpEn while SNP is active; disable
+	 * hotplug here and re-enable it in snp_shutdown().
+	 */
+	cpu_hotplug_disable();
 
 	if (!cpumask_equal(cpu_online_mask, cpu_present_mask)) {
-		ret = -EOPNOTSUPP;
+		cpu_hotplug_enable();
 		pr_warn("SNP init failed: not all CPUs online. (%*pbl online <-> %*pbl present masks).\n",
 			cpumask_pr_args(cpu_online_mask),
 			cpumask_pr_args(cpu_present_mask));
-		goto unlock;
+		return -EOPNOTSUPP;
 	}
 
 	wbinvd_on_all_cpus();

@@ -548,12 +551,7 @@ int snp_prepare(void)
 	/* SNP_INIT requires MSR_VM_HSAVE_PA to be cleared on all CPUs. */
 	on_each_cpu(clear_hsave_pa, NULL, 1);
 
-	ret = 0;
-
-unlock:
-	cpus_read_unlock();
-
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL_FOR_MODULES(snp_prepare, "ccp");
 

@@ -567,6 +565,13 @@ void snp_shutdown(void)
 
 	clear_rmp();
 	on_each_cpu(mfd_reconfigure, NULL, 1);
+
+	/*
+	 * The firmware has disabled SNP (SnpEn is clear), so re-enable CPU
+	 * hotplug.  A legacy SNP shutdown returns above with SnpEn still set and
+	 * leaves hotplug disabled.
+	 */
+	cpu_hotplug_enable();
 }
 EXPORT_SYMBOL_FOR_MODULES(snp_shutdown, "ccp");
 

@@ -577,6 +582,8 @@ EXPORT_SYMBOL_FOR_MODULES(snp_shutdown, "ccp");
  */
 int __init snp_rmptable_init(void)
 {
+	u64 val;
+
 	if (WARN_ON_ONCE(!cc_platform_has(CC_ATTR_HOST_SEV_SNP)))
 		return -ENOSYS;
 

@@ -586,6 +593,15 @@ int __init snp_rmptable_init(void)
 	if (!setup_rmptable())
 		return -ENOSYS;
 
+	/*
+	 * On a kexec boot SNP may already be enabled (legacy firmware leaves
+	 * SnpEn set across shutdown), in which case snp_prepare() bails without
+	 * disabling CPU hotplug, so disable it here.
+	 */
+	rdmsrq(MSR_AMD64_SYSCFG, val);
+	if (val & MSR_AMD64_SYSCFG_SNP_EN)
+		cpu_hotplug_disable();
+
 	/*
 	 * Setting crash_kexec_post_notifiers to 'true' to ensure that SNP panic
 	 * notifier is invoked to do SNP IOMMU shutdown before kdump.

2.43.0

You're right that the suspend path bypasses cpu_hotplug_disable() — freeze_secondary_cpus() uses _cpu_down() directly and ignores the cpu_hotplug_disabled counter. But this is neither introduced nor affected by this patch, and does not apply to SNP hosts:

1. This patch does not touch the suspend/resume path. cpu_hotplug_disable() holds the online CPU set stable against the regular (sysfs) hotplug path while SNP is active. The cpus_read_lock() this patch replaces did not gate the freeze/thaw path either, so suspend/resume behaviour is unchanged from base SNP.
2. SNP hosts do not support system suspend/resume. It is not a supported configuration for an SNP‑enabled host, and there is no path today to re‑establish the per‑CPU SNP state (SnpEn) on resume — snp_enable() has never been registered as a CPU‑hotplug/resume callback. That is a pre‑existing property of base SNP, independent of this series.

Thanks,
Ashish

From: Ashish Kalra <[email protected]>

The new RMPOPT instruction helps manage per-CPU RMP optimization structures inside the CPU. It takes a 1GB-aligned physical address and either returns the status of the optimizations or tries to enable the optimizations.

Per-CPU RMPOPT tables support at most 2 TB of addressable memory for RMP optimizations.

Initialize the per-CPU RMPOPT table base to the starting physical address. This enables RMP optimization for up to 2 TB of system RAM on all CPUs.

Additionally, add support to setup and enable RMPOPT once SNP is enabled and initialized.

---
v14: rmpopt_disable() and the RMPOPT_BASE teardown were removed from this
patch (the disable path is reworked in the next patch, and the MSRs are now left in place on shutdown). Dropped Reviewed-by: Dave Hansen and Tom Lendacky due to this rework.

 arch/x86/include/asm/msr-index.h |  3 +++
 arch/x86/include/asm/sev.h       |  2 ++
 arch/x86/virt/svm/sev.c          | 46 ++++++++++++++++++++++++++++----
 drivers/crypto/ccp/sev-dev.c     |  2 ++
 4 files changed, 48 insertions(+), 5 deletions(-)

index 3a8e51a0c9e8..1635e2e1c576 100644
@@ -761,6 +761,9 @@
 #define MSR_AMD64_SEG_RMP_ENABLED_BIT	0
 #define MSR_AMD64_SEG_RMP_ENABLED	BIT_ULL(MSR_AMD64_SEG_RMP_ENABLED_BIT)
 #define MSR_AMD64_RMP_SEGMENT_SHIFT(x)	(((x) & GENMASK_ULL(13, 8)) >> 8)
+#define MSR_AMD64_RMPOPT_BASE		0xc0010139
+#define MSR_AMD64_RMPOPT_ENABLE_BIT	0
+#define MSR_AMD64_RMPOPT_ENABLE		BIT_ULL(MSR_AMD64_RMPOPT_ENABLE_BIT)
 
 #define MSR_SVSM_CAA			0xc001f000
 

index 9e7a077c445d..5638d09b5132 100644
@@ -662,6 +662,7 @@ static inline void snp_leak_pages(u64 pfn, unsigned int pages)
 	__snp_leak_pages(pfn, pages, true);
 }
 int snp_prepare(void);
+void snp_setup_rmpopt(void);
 void snp_shutdown(void);
 #else
 static inline bool snp_probe_rmptable_info(void) { return false; }

@@ -680,6 +681,7 @@ static inline void snp_leak_pages(u64 pfn, unsigned int npages) {}
 static inline void kdump_sev_callback(void) { }
 static inline void snp_fixup_e820_tables(void) {}
 static inline int snp_prepare(void) { return -ENODEV; }
+static inline void snp_setup_rmpopt(void) {}
 static inline void snp_shutdown(void) {}
 #endif
 

index f833cb7e4da3..287a8345854b 100644
@@ -1663,6 +1663,8 @@ static int __sev_snp_init_locked(int *error, unsigned int max_snp_asid)
 
 	sev_es_tmr_size = SNP_TMR_SIZE;
 
+	snp_setup_rmpopt();
+
 	return 0;
 }
 

2.43.0

From: Ashish Kalra <[email protected]>

When SNP is enabled, all writes to memory are checked to ensure memory integrity. This imposes performance overhead on the whole system.

RMPOPT is a new instruction that minimizes the performance overhead of RMP checks on the hypervisor and on non-SNP guests by allowing RMP checks to be skipped for 1GB regions of memory that are known not to contain any SNP guest memory.

Add support for performing RMP optimizations asynchronously using a dedicated workqueue.

At RMP initialization time, run an optimization pass over all physical memory (up to 2TB of system RAM, starting from the lowest physical memory address aligned down to a 1GB boundary), skipping RMP checks for 1GB regions that do not contain SNP guest memory (excluding preassigned pages such as the RMP table and firmware pages).

As SNP guests are launched, RMPUPDATE assigns their private pages to guest-owned state; when such a page falls within an optimized 1GB region, the hardware clears that region's RMPOPT optimization and RMP checks resume there to protect the guest memory.

Since launching SNP guests clears these optimizations, perform them again asynchronously using the dedicated workqueue.

---
v14: Reworked the setup/teardown - initialize once and do not tear it down;
rmpopt_disable() now only cancels the pending pass. Use a dedicated per-CPU workqueue (WQ_PERCPU) and drop the migrate_disable()/ migrate_enable() around the local scan. Added a binutils-version comment above the RMPOPT .byte and trimmed redundant comments and the 2 TB pr_info(). Subject reworded from "Add support to perform RMP optimizations asynchronously". Dropped Reviewed-by: Ackerley Tng and Tom Lendacky due to the rework (kept Suggested-by).

 arch/x86/virt/svm/sev.c | 92 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 91 insertions(+), 1 deletion(-)

index a059327dc107..35678b1f535d 100644
@@ -19,6 +19,7 @@
 #include <linux/iommu.h>
 #include <linux/amd-iommu.h>
 #include <linux/nospec.h>
+#include <linux/workqueue.h>
 
 #include <asm/sev.h>
 #include <asm/processor.h>

@@ -124,7 +125,16 @@ static void *rmp_bookkeeping __ro_after_init;
 
 static u64 probed_rmp_base, probed_rmp_size;
 
-static phys_addr_t rmpopt_pa_start;
+static u64 rmpopt_pa_start, rmpopt_pa_end;
+
+enum rmpopt_op_type {
+	RMPOPT_OP_VERIFY_AND_REPORT_STATUS,
+	RMPOPT_OP_REPORT_STATUS
+};
+
+static struct workqueue_struct *rmpopt_wq;
+static struct delayed_work rmpopt_delayed_work;
+static DEFINE_MUTEX(rmpopt_wq_mutex);
 
 static LIST_HEAD(snp_leaked_pages_list);
 static DEFINE_SPINLOCK(snp_leaked_pages_list_lock);

@@ -557,6 +567,14 @@ int snp_prepare(void)
 }
 EXPORT_SYMBOL_FOR_MODULES(snp_prepare, "ccp");
 
+static void rmpopt_disable(void)
+{
+	guard(mutex)(&rmpopt_wq_mutex);
+
+	if (rmpopt_wq)
+		cancel_delayed_work_sync(&rmpopt_delayed_work);
+}
+
 void snp_shutdown(void)
 {
 	u64 syscfg;

@@ -565,6 +583,8 @@ void snp_shutdown(void)
 	if (syscfg & MSR_AMD64_SYSCFG_SNP_EN)
 		return;
 
+	rmpopt_disable();
+
 	clear_rmp();
 	on_each_cpu(mfd_reconfigure, NULL, 1);
 

@@ -583,6 +603,43 @@ static bool rmpopt_capable(void)
 	       cc_platform_has(CC_ATTR_HOST_SEV_SNP);
 }
 
+/*
+ * RMPOPT optimizations skip RMP checks at 1GB granularity if this range of
+ * memory does not contain any SNP guest memory.
+ *
+ * @pa is a system physical address; RMPOPT operates on the containing 1GB.
+ */
+static void rmpopt(u64 pa)
+{
+	enum rmpopt_op_type op = RMPOPT_OP_VERIFY_AND_REPORT_STATUS;
+	u64 pa_start = ALIGN_DOWN(pa, SZ_1G);
+
+	/* Supported by binutils 2.48+ */
+	asm volatile(".byte 0xf2, 0x0f, 0x01, 0xfc"
+		     :: "a" (pa_start), "c" (op)
+		     : "memory", "cc");
+}
+
+/* on_each_cpu() callback: optimize the whole RMPOPT range on this CPU. */
+static void rmpopt_scan_range(void *arg)
+{
+	u64 pa;
+
+	for (pa = rmpopt_pa_start; pa < rmpopt_pa_end; pa += SZ_1G)
+		rmpopt(pa);
+}
+
+static void do_rmpopt_work(struct work_struct *work)
+{
+	/*
+	 * Warm up the RMPOPT cache on this pinned per-CPU worker with interrupts
+	 * on, so the IRQ-disabled fan-out below only issues cache-hit RMPOPTs.
+	 */
+	rmpopt_scan_range(NULL);
+
+	on_each_cpu_mask(cpu_primary_thread_mask, rmpopt_scan_range, NULL, true);
+}
+
 void snp_setup_rmpopt(void)
 {
 	u64 rmpopt_base;

@@ -591,6 +648,30 @@ void snp_setup_rmpopt(void)
 	if (!rmpopt_capable())
 		return;
 
+	guard(mutex)(&rmpopt_wq_mutex);
+
+	/*
+	 * Set up once: the workqueue and RMPOPT_BASE MSRs are left in place on
+	 * shutdown, so a later re-initialization just re-queues the optimization
+	 * pass rather than redoing the setup.
+	 */
+	if (rmpopt_wq) {
+		queue_delayed_work(rmpopt_wq, &rmpopt_delayed_work, 0);
+		return;
+	}
+
+	/*
+	 * Use a dedicated per-CPU workqueue so the potentially lengthy warm-up
+	 * scan does not tie up a shared workqueue worker.
+	 */
+	rmpopt_wq = alloc_workqueue("rmpopt_wq", WQ_PERCPU, 1);
+	if (!rmpopt_wq) {
+		pr_err("Failed to allocate RMPOPT workqueue\n");
+		return;
+	}
+
+	INIT_DELAYED_WORK(&rmpopt_delayed_work, do_rmpopt_work);
+
 	rmpopt_pa_start = ALIGN_DOWN(PFN_PHYS(min_low_pfn), SZ_1G);
 	rmpopt_base = rmpopt_pa_start | MSR_AMD64_RMPOPT_ENABLE;
 

@@ -600,6 +681,15 @@ void snp_setup_rmpopt(void)
 	 */
 	for_each_cpu(cpu, cpu_primary_thread_mask)
 		wrmsrq_on_cpu(cpu, MSR_AMD64_RMPOPT_BASE, rmpopt_base);
+
+	rmpopt_pa_end = ALIGN(PFN_PHYS(max_pfn), SZ_1G);
+
+	if ((rmpopt_pa_end - rmpopt_pa_start) > SZ_2T)
+		rmpopt_pa_end = rmpopt_pa_start + SZ_2T;
+
+	queue_delayed_work(rmpopt_wq, &rmpopt_delayed_work, 0);
+
+	pr_info("RMPOPT optimizations enabled\n");
 }
 EXPORT_SYMBOL_FOR_MODULES(snp_setup_rmpopt, "ccp");
 

2.43.0

RMPOPT's only output is the carry flag (RFLAGS.CF); it does not modify %rax. The VERIFY_AND_REPORT_STATUS result is returned in CF, not %rax — unlike RMPREAD/PSMASH/RMPUPDATE, which return data in registers. Since RMPOPT leaves %rax unchanged, the input‑only "a" (pa_start) constraint is correct and no output/clobber for %rax is required; the loop counter cannot be corrupted.

The premise that the RMPOPT caches are strictly per‑CPU is not correct. The RMPOPT optimization results are held in shared memory, not in per‑CPU caches. Once the warm‑up pass on the local CPU — run with interrupts enabled and preemptible — has verified and recorded the 1GB regions, the follower CPUs read those already‑computed results from shared memory, so their RMPOPTs short‑circuit instead of re‑scanning the RMP. This is why the fan‑out is cheap: measured via the debug follower_timings node, the worst‑case follower IPI callback completes in ≈1.3 ms (1,341,505 ns) — roughly four orders of magnitude below the soft‑lockup/NMI‑watchdog thresholds— confirming the followers do not each perform a cold up‑to‑2TB scan in hardirq.

CPU hotplug is disabled the entire time SNP is active (patch 2/5), so a CPU's RMPOPT_BASE can only be reset by a hotplug cycle that occurs after a full SNP shutdown has cleared SnpEn and re‑enabled hotplug.
RMPOPT is set up once and left in place; re‑initialization simply re‑queues the optimization pass rather than reprogramming the MSRs. Guarding against a full‑shutdown + CPU‑hotplug + SNP‑re‑init sequence is outside the supported flow, so the setup is intentionally not re‑done on re‑initialization.

Thanks,
Ashish

Hello Boris,

Thanks, Boris. Splitting setup from start and collapsing to a single export makes sense — a couple of constraints from the RMPOPT spec shape how it has to be done.

RMPOPT_BASE can only be written (RMPOPT_EN set) when SYSCFG[SnpEn] and RMP_CFG[SegmentedRmpEn] are both 1; otherwise the access #GP(0)s. So the MSR programming can't run from an init‑time initcall — SnpEn is 0 then and it would #GP. The software setup can, though, so the split becomes:

- an initcall in this file does the software setup — allocate the workqueue and INIT_DELAYED_WORK(), no export;
- snp_enable_rmpopt() (the single export) programs RMPOPT_BASE on the primary threads and queues the pass. ccp calls it after it has enabled SNP, and kvm‑amd calls it on teardown.

The same spec text makes that single entry point safe to call repeatedly: RMPOPT_BASE_ADDR is read‑only once RMPOPT_EN is 1 (and RMPOPT_EN can't be cleared while SnpEn is 1), so a later call's write is a probably a no‑op rather than a reprogram. If we want to avoid even the redundant IPIs, snp_enable_rmpopt() can read RMPOPT_BASE and skip programming when RMPOPT_EN is already set — a hardware‑state check instead of an if (rmpopt_wq).

On clearing X86_FEATURE_RMPOPT when the allocation fails: that hits the problem we ran into in earlier revisions — the workqueue allocation is at initcall time, after alternatives are patched, where setup_clear_cpu_cap() isn't reliable (static_cpu_has() is already baked in), so clearing the cap won't flip rmpopt_capable(). The setup/enable split removes most of the if (rmpopt_wq) checks anyway; the only one left is a single guard in snp_enable_rmpopt() for the (rare) allocation‑failure case, which I will probably like to keep rather than rely on clearing the feature.

I'll respin as v15 with the setup/enable split once we settle the feature‑clear question and the RMPOPT_BASE MSR programming question (i.e., skipping it if RMPOPT_EN is already set).

Yes, i will fix the comments as below.

Thanks,
Ashish

This programming sure sounds like something we don't need to repeat each time we enable RMPOPT...

rmpopt_pa_start is practically static so I'd love it if those MSRs are written once and that's it. The question is, do they keep their value when we disable SNP?

And I can basically imagine the answer from hw folks: "yeah, yeah, maybe, but to be on the safe side, you should always write them after having enabled SNP."

Because if not, I'd be perfectly fine with us setting them on the *first* SNP init and not touching them again.

IOW, this pseudo:

	if (!rdmsr(RMPOPT_BASE))
		wrmsr(RMPOPT_BASE, ...):

This should probably be in the snp_enable_rmpopt() function anyway as it should do what we want.

Yap, or that. Sounds ok to me if it works.

Or, you can introduce that bool rmpopt_enabled and clear it and test it in rmpopt_capable(). As long as it stays a static var, only visible in this compilation unit and not exported, that's good enough.

Thx.

Btw, you can respin the last two patches only and send them as a reply to that thread - I have applied the first 3 already so no need to resend them again.

Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

Hello Boris,

One thing to sort out first, since you've already applied p1‑p3: the setup/enable rework reshapes a few things that landed in p3 — snp_setup_rmpopt() becomes the single snp_enable_rmpopt() export, rmpopt_capable() now uses the rmpopt_enabled guard, and the ccp caller in sev-dev.c changes with the rename. I can carry all of that as deltas in the respun p4 (i.e. p3 adds snp_setup_rmpopt() and p4 renames/reworks it right after), but if you'd rather it land cleanly I can refresh p3 too so it introduces the final shape. Which would you prefer — p4 deltas over what's applied, or a refreshed p3 as well?

Thanks,
Ashish

Nah, feel free to send a new set, if you have to touch 1-3.

Thx.

Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette

From: Ashish Kalra <[email protected]>

The RMPOPT table is a per-CPU table which indicates whether 1GB regions of physical memory are entirely hypervisor-owned.

When performing host memory accesses in hypervisor mode as well as non-SNP guest mode, the processor may consult the RMPOPT table to potentially skip an RMP access and improve performance.

Normal guest events disable RMP optimizations: pages are converted from shared to private as SNP guests are launched, and large pages are split and collapsed during guest operation -- both disable the RMPOPT optimizations for the affected 1GB regions.

When guests are torn down, their pages are converted back to shared, so those regions may become eligible for RMPOPT optimization again. Without some intervention, all RMP optimizations would eventually be lost, so re-optimize all of physical memory on SNP guest teardown.

Perform the re-optimization after a delay, using mod_delayed_work() so that the delay timer is reset on each call. This batches multiple guest terminations into a single pass: the re-optimization runs 10 seconds after the *last* termination rather than after the first. mod_delayed_work() also re-queues work that is already in-flight, so a re-scan request during an active scan is not silently dropped.

Guest teardown is currently the only event that returns guest memory to hypervisor ownership: SNP guests do not support ballooning or memory hotplug, so pages freed during a guest's lifetime remain guest-owned. It is therefore the only point at which memory becomes eligible for RMP re-optimization, which is why re-optimization is driven by guest teardown rather than by a periodic scan.

---
 arch/x86/include/asm/sev.h |  2 ++
 arch/x86/kvm/svm/sev.c     |  2 ++
 arch/x86/virt/svm/sev.c    | 31 +++++++++++++++++++++++++++++++
 3 files changed, 35 insertions(+)

index 5638d09b5132..3235e171647d 100644
@@ -662,6 +662,7 @@ static inline void snp_leak_pages(u64 pfn, unsigned int pages)
 	__snp_leak_pages(pfn, pages, true);
 }
 int snp_prepare(void);
+void snp_rmpopt_all_physmem(void);
 void snp_setup_rmpopt(void);
 void snp_shutdown(void);
 #else

@@ -681,6 +682,7 @@ static inline void snp_leak_pages(u64 pfn, unsigned int npages) {}
 static inline void kdump_sev_callback(void) { }
 static inline void snp_fixup_e820_tables(void) {}
 static inline int snp_prepare(void) { return -ENODEV; }
+static inline void snp_rmpopt_all_physmem(void) {}
 static inline void snp_setup_rmpopt(void) {}
 static inline void snp_shutdown(void) {}
 #endif

index 5705723f1f41..d8e6b8a08b79 100644
@@ -3032,6 +3032,8 @@ void sev_vm_destroy(struct kvm *kvm)
 		 */
 		if (snp_decommission_context(kvm))
 			return;
+
+		snp_rmpopt_all_physmem();
 	} else {
 		sev_unbind_asid(kvm, sev->handle);
 	}

index 35678b1f535d..c16f82642390 100644
@@ -640,6 +640,37 @@ static void do_rmpopt_work(struct work_struct *work)
 	on_each_cpu_mask(cpu_primary_thread_mask, rmpopt_scan_range, NULL, true);
 }
 
+/*
+ * Delay, in milliseconds, before the RMP re-optimization pass runs after an SNP
+ * guest is torn down, passed as the delay to mod_delayed_work().  This coalesces
+ * a burst of teardowns into a single scan and gives each guest's pages time to
+ * be converted back to the shared, hypervisor-owned state.  The 10 second value
+ * is a heuristic trading re-optimization latency against scanning too eagerly.
+ */
+#define RMPOPT_WORK_TIMEOUT	(10 * MSEC_PER_SEC)
+
+/*
+ * Perform RMP optimizations on memory freed by terminating guests.  The scan
+ * is deferred, so it normally runs after sev_gmem_invalidate() has converted
+ * this guest's pages back to shared, and picks them up then.  A very large
+ * guest whose conversion has not finished by then is picked up by a later
+ * teardown's scan.
+ */
+void snp_rmpopt_all_physmem(void)
+{
+	if (!rmpopt_capable())
+		return;
+
+	guard(mutex)(&rmpopt_wq_mutex);
+
+	if (!rmpopt_wq)
+		return;
+
+	mod_delayed_work(rmpopt_wq, &rmpopt_delayed_work,
+			 msecs_to_jiffies(RMPOPT_WORK_TIMEOUT));
+}
+EXPORT_SYMBOL_FOR_MODULES(snp_rmpopt_all_physmem, "kvm-amd");
+
 void snp_setup_rmpopt(void)
 {
 	u64 rmpopt_base;

2.43.0

The concern is valid in principle. In practice, though, it requires an unsupported configuration:

- A full SNP shutdown (SNP_SHUTDOWN, which clears SnpEn) only succeeds when there are no active SNP guests. The only way snp_rmpopt_all_physmem() can re‑queue the pass after SnpEn has been cleared is if the CCP/SEV platform is being torn down (driver unbind/removal or system shutdown) concurrently with an in‑flight SNP guest teardown.
- Tearing down the SEV platform while SNP guests are still being destroyed is not a supported operation.

Given that, we keep the RMPOPT setup/teardown minimal — set up once, and re‑queue the pass only on re‑initialization — rather than add persistent "enabled" state solely to guard an unsupported teardown ordering.

Thanks,
Ashish

The RMPOPT optimization results are held in shared memory, not per‑CPU caches, so after the local warm‑up the follower CPUs read the already‑computed results from shared memory and short‑circuit. Measured via follower_timings, the worst‑case follower IPI callback is ≈1.3 ms (1,341,505 ns) — ~4 orders of magnitude under the soft‑lockup/NMI/RCU‑stall thresholds.

Thanks,
Ashish