x86/Hyper-V: Add SEV negotiate protocol support in Isolation VM

From: Tianyu Lan <[email protected]>

Hyper-V Isolation VM code uses sev_es_ghcb_hv_call() to read/write MSR via GHCB page. The SEV-ES guest should negotiate GHCB version before reading/writing MSR via GHCB page. Expose sev_es_negotiate_protocol() and sev_es_terminate() from AMD SEV code and negotiate GHCB version in hyperv_init_ghcb() fro Hyper-V Isolation VM.

Signed-off-by Tianyu Lan <[email protected]>

---
 arch/x86/hyperv/hv_init.c    | 8 ++++++++
 arch/x86/include/asm/sev.h   | 6 ++++++
 arch/x86/kernel/sev-shared.c | 4 ++--
 3 files changed, 16 insertions(+), 2 deletions(-)

arch/x86/hyperv/hv_init.c +8 -0

index 8b392b6b7b93..56e2c34e7d64 100644
@@ -29,6 +29,7 @@
 #include <clocksource/hyperv_timer.h>
 #include <linux/highmem.h>
 #include <linux/swiotlb.h>
+#include <asm/sev.h>
 
 int hyperv_init_cpuhp;
 u64 hv_current_partition_id = ~0ull;

@@ -70,6 +71,13 @@ static int hyperv_init_ghcb(void)
 	ghcb_base = (void **)this_cpu_ptr(hv_ghcb_pg);
 	*ghcb_base = ghcb_va;
 
+	/* Negotiate GHCB Version. */
+	if (!sev_es_negotiate_protocol())
+		sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SEV_ES_PROT_UNSUPPORTED);
+
+	/* Write ghcb page back after negotiating protocol. */
+	wrmsrl(MSR_AMD64_SEV_ES_GHCB, ghcb_gpa);
+	VMGEXIT();
 	return 0;
 }
 

arch/x86/include/asm/sev.h +6 -0

index 19514524f0f8..ad69c1dc081b 100644
@@ -161,6 +161,9 @@ extern enum es_result sev_es_ghcb_hv_call(struct ghcb *ghcb,
 					  struct es_em_ctxt *ctxt,
 					  u64 exit_code, u64 exit_info_1,
 					  u64 exit_info_2);
+extern bool sev_es_negotiate_protocol(void);
+extern void sev_es_terminate(unsigned int set, unsigned int reason);
+
 static inline int rmpadjust(unsigned long vaddr, bool rmp_psize, unsigned long attrs)
 {
 	int rc;

@@ -226,6 +229,9 @@ static inline int snp_issue_guest_request(u64 exit_code, struct snp_req_data *in
 {
 	return -ENOTTY;
 }
+
+static bool sev_es_negotiate_protocol(void) { return false; }
+static void sev_es_terminate(unsigned int set, unsigned int reason) { }
 #endif
 
 #endif

arch/x86/kernel/sev-shared.c +2 -2

index 2b4270d5559e..bffc38f0d5ed 100644
@@ -86,7 +86,7 @@ static bool __init sev_es_check_cpu_features(void)
 	return true;
 }
 
-static void __noreturn sev_es_terminate(unsigned int set, unsigned int reason)
+void __noreturn sev_es_terminate(unsigned int set, unsigned int reason)
 {
 	u64 val = GHCB_MSR_TERM_REQ;
 

@@ -137,7 +137,7 @@ static void snp_register_ghcb_early(unsigned long paddr)
 		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_REGISTER);
 }
 
-static bool sev_es_negotiate_protocol(void)
+bool sev_es_negotiate_protocol(void)
 {
 	u64 val;
 

Signature · 1 line

2.25.1

Quoted 9 lines · Tianyu Lan

From: Tianyu Lan <[email protected]>

Hyper-V Isolation VM code uses sev_es_ghcb_hv_call() to read/write MSR via GHCB page. The SEV-ES guest should negotiate GHCB version before reading/writing MSR via GHCB page. Expose sev_es_negotiate_protocol() and sev_es_terminate() from AMD SEV code and negotiate GHCB version in hyperv_init_ghcb() fro Hyper-V Isolation VM.

Signed-off-by Tianyu Lan <[email protected]>

Applied to tip's x86/sev and checked that this can fix the regression (to be introduced) by commit 2ea29c5abbc2 ("x86/sev: Save the negotiated GHCB version"):

Tested-by Andrea Parri (Microsoft) <[email protected]>

Nits: (in the commit message) fro -> for, Isolation VM -> Isolated VM

From: Tianyu Lan <[email protected]>

Hyper-V Isolation VM code uses sev_es_ghcb_hv_call() to read/write MSR via GHCB page. The SEV-ES guest should negotiate GHCB version before reading/writing MSR via GHCB page.

Expose sev_es_negotiate_protocol() and sev_es_terminate() from AMD SEV code

Quoted 5 lines · Tianyu Lan

From: Tianyu Lan <[email protected]>

Hyper-V Isolation VM code uses sev_es_ghcb_hv_call() to read/write MSR via GHCB page. The SEV-ES guest should negotiate GHCB version before reading/writing MSR via GHCB page.

Why is that?

Quoted 2 lines

Expose sev_es_negotiate_protocol() and sev_es_terminate() from AMD SEV code

Yeah, you keep wanting to expose random SEV-specific code and when we go and change it in the future, you'll come complaining that we broke hyperv.

I think it might be a lot better if you implement your own functions:
for example, looking at sev_es_negotiate_protocol() - it uses only primitives which you can use because, well, VMGEXIT() is simply a wrapper around the asm insn and sev_es_wr_ghcb_msr() is simply writing into the MSR.

Ditto for sev_es_terminate().

And sev_es_ghcb_hv_call() too, for that matter. You can define your own.

IOW, you're much better off using those primitives and creating your own functions than picking out random SEV-functions and then us breaking your isolation VM stuff.