Support generic disabling of all XSAVE features
For performance testing and debugging it can be useful to disable XSAVE features individually.
This patchkit hooks up XSAVE with the generic clearcpuid=... option, so that disabling a CPUID feature automatically disables the respective XSAVE feature.
It also cleans up CPUID dependency management. Currently it's possible to generate configurations with cleacpuid that crash.
It replaces an earlier patchkit that did this with special case options.
v1:
Initial post
v2:
Work around broken lguest by exporting set_cpu_cap Repost with cover letter
v3:
Repost. No changes to code.
v4:
Rebase to latest tree. Repost.
v5:
Fix dependency algorithm. Clean dups in table. Rebase. v6:
Rebase. No changes to code.
v7:
Rebase. No changes to code.
PATCH v7 1/5 x86/xsave: Move xsave initialization to after parsing early parameters
From: Andi Kleen <[email protected]>
Move the XSAVE initialization code to be after parsing early parameters. I don't see any reason why the FPU code needs to be initialized that early, nothing else in the initialization phase uses XSAVE. This is useful to be able to handle command line parameters in the XSAVE initialization code.
--- arch/x86/kernel/cpu/common.c | 2 -- arch/x86/kernel/setup.c | 3 +++ 2 files changed, 3 insertions(+), 2 deletions(-)
arch/x86/kernel/cpu/common.c +0 -2
@@ -903,8 +903,6 @@ static void __init early_identify_cpu(struct cpuinfo_x86 *c) }setup_force_cpu_cap (X86_FEATURE_ALWAYS ); -fpu__init_system (c); -#ifdef CONFIG_X86_32 /* * Regardless of whether PCID is enumerated, the SDM says
arch/x86/kernel/setup.c +3 -0
@@ -92,6 +92,7 @@#include <asm/processor.h> #include <asm/bugs.h> #include <asm/kasan.h> +#include <asm/fpu/internal.h> #include <asm/vsyscall.h> #include <asm/cpu.h>
@@ -992,6 +993,8 @@ void __init setup_arch(char **cmdline_p)parse_early_param (); +fpu__init_system (&boot_cpu_data); +#ifdef CONFIG_MEMORY_HOTPLUG /* * Memory used by the kernel cannot be hot-removed because Linux
Signature · 1 line
2.13.6
Re: [PATCH v7 1/5] x86/xsave: Move xsave initialization to after parsing early parameters
Quoted 9 lines · Andi Kleen
From: Andi Kleen <[email protected]>
Move the XSAVE initialization code to be after parsing early parameters. I don't see any reason why the FPU code needs to be initialized that early, nothing else in the initialization phase uses XSAVE. This is useful to be able to handle command line parameters in the XSAVE initialization code.
Signed-off-by Andi Kleen <[email protected]>
PATCH v7 2/5 x86/cpuid: Add generic table for cpuid dependencies
In reply to Andi KleenFrom: Andi Kleen <[email protected]>
Some CPUID features depend on other features. Currently it's possible to to clear dependent features, but not clear the base features, which can cause various interesting problems.
This patch implements a generic table to describe dependencies between CPUID features, to be used by all code that clears CPUID.
Some subsystems (like XSAVE) had an own implementation of this, but it's better to do it all in a single place for everyone.
Then clear_cpu_cap and setup_clear_cpu_cap always look up this table and clear all dependencies too.
This is intended to be a practical table: only for features that make sense to clear. If someone for example clears FPU, or other features that are essentially part of the required base feature set, not much is going to work. Handling that is right now out of scope. We're only handling features which can be usefully cleared.
v2: Add EXPORT_SYMBOL for clear_cpu_id for lguest
v3:
Fix handling of depending issues
Fix dups in the table (Jonathan McDowell)
--- arch/x86/include/asm/cpufeature.h | 8 +++- arch/x86/include/asm/cpufeatures.h | 5 ++ arch/x86/kernel/cpu/Makefile | 1 + arch/x86/kernel/cpu/cpuid-deps.c | 94 ++++++++++++++++++++++++++++++++++++++ 4 files changed, 106 insertions(+), 2 deletions(-) create mode 100644 arch/x86/kernel/cpu/cpuid-deps.c
arch/x86/include/asm/cpufeature.h +6 -2
@@ -125,8 +125,12 @@ extern const char * const x86_bug_flags[NBUGINTS*32];#define boot_cpu_has (bit) cpu_has(&boot_cpu_data, bit)#define set_cpu_cap (c, bit) set_bit(bit, (unsigned long *)((c)->x86_capability)) -#define clear_cpu_cap (c, bit) clear_bit(bit, (unsigned long *)((c)->x86_capability)) -#define setup_clear_cpu_cap (bit) do { \ +#define __clear_cpu_cap (c, bit) clear_bit(bit, (unsigned long *)((c)->x86_capability)) + +extern void setup_clear_cpu_cap (int bit); +extern void clear_cpu_cap (struct cpuinfo_x86 *cpu,int bit); + +#define __setup_clear_cpu_cap (bit) do { \ clear_cpu_cap(&boot_cpu_data, bit); \ set_bit(bit, (unsigned long *)cpu_caps_cleared); \ } while (0)
arch/x86/include/asm/cpufeatures.h +5 -0
@@ -21,6 +21,11 @@* this feature bit is not displayed in /proc/cpuinfo at all. */ +/* +* When adding new features here that depend on other features, +* please update the table in kernel/cpu/cpuid-deps.c +*/ +/* Intel-defined CPU features, CPUID level 0x00000001 (edx), word 0 */ #define X86_FEATURE_FPU ( 0*32+ 0)/* Onboard FPU */ #define X86_FEATURE_VME ( 0*32+ 1)/* Virtual Mode Extensions */
arch/x86/kernel/cpu/Makefile +1 -0
@@ -22,6 +22,7 @@ obj-y += rdrand.o obj-y += match.o obj-y += bugs.o obj-$(CONFIG_CPU_FREQ) += aperfmperf.o +obj-y += cpuid-deps.o obj-$(CONFIG_PROC_FS) += proc.o obj-$(CONFIG_X86_FEATURE_NAMES) += capflags.o powerflags.o
arch/x86/kernel/cpu/cpuid-deps.c new file +94 -0
94 lines not on this page · raw message
Signature · 1 line
2.13.6
Re: [PATCH v7 2/5] x86/cpuid: Add generic table for cpuid dependencies
On Wed, 4 Oct 2017, Andi Kleen wrote:
Quoted 1 line
v2: Add
EXPORT_SYMBOLforclear_cpu_idfor lguest
clear_cpu_id? You probably mean clear_cpu_cap, but that's moot now that lguest is gone......
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
...
arch/x86/include/asm/cpufeature.h extern const char * const x86_bug_flags[NBUGINTS*32]; · line 136
Quoted 13 lines
#define
set_cpu_cap(c, bit)set_bit(bit, (unsigned long *)((c)->x86_capability))arch/x86/include/asm/cpufeature.h +6
-2-#define clear_cpu_cap (c, bit) clear_bit(bit, (unsigned long *)((c)->x86_capability)) -#define setup_clear_cpu_cap (bit) do { \ +#define __clear_cpu_cap (c, bit) clear_bit(bit, (unsigned long *)((c)->x86_capability)) + +extern void setup_clear_cpu_cap (int bit); +extern void clear_cpu_cap (struct cpuinfo_x86 *cpu,int bit); + +#define __setup_clear_cpu_cap (bit) do { \ clear_cpu_cap(&boot_cpu_data, bit); \ set_bit(bit, (unsigned long *)cpu_caps_cleared); \ } while (0)
__clear_cpu_cap() and __setup_clear_cpu_cap() should not be in the header file. They should be in the new cpuid-deps file so they are not exposed. While at it please implement them as inlines. There is no reason for having them as macros.
Quoted 45 lines
arch/x86/kernel/cpu/cpuid-deps.c new file +42
-0@@ -0,0 +1,94 @@ +/* Declare dependencies between CPUIDs */ +#include <linux/kernel.h> +#include <linux/init.h> +#include <linux/module.h> +#include <asm/cpufeature.h> + +struct cpuid_dep { +int feature; +int disable; +}; + +/* +* Table of CPUID features that depend on others. +* +* This only includes dependencies that can be usefully disabled, not +* features part of the base set (like FPU). +*/ +const static struct cpuid_dep cpuid_deps[] = { + {X86_FEATURE_XSAVE ,X86_FEATURE_XSAVEOPT }, + {X86_FEATURE_XSAVE ,X86_FEATURE_XSAVEC }, + {X86_FEATURE_XSAVE ,X86_FEATURE_XSAVES }, + {X86_FEATURE_XSAVE ,X86_FEATURE_AVX }, + {X86_FEATURE_XSAVE ,X86_FEATURE_AVX512F }, + {X86_FEATURE_XSAVE ,X86_FEATURE_PKU }, + {X86_FEATURE_XSAVE ,X86_FEATURE_MPX }, + {X86_FEATURE_XSAVE ,X86_FEATURE_XGETBV1 }, + {X86_FEATURE_XMM ,X86_FEATURE_XMM2 }, + {X86_FEATURE_XMM2 ,X86_FEATURE_XMM3 }, + {X86_FEATURE_XMM2 ,X86_FEATURE_XMM4_1 }, + {X86_FEATURE_XMM2 ,X86_FEATURE_XMM4_2 }, + {X86_FEATURE_XMM2 ,X86_FEATURE_XMM3 }, + {X86_FEATURE_XMM2 ,X86_FEATURE_PCLMULQDQ }, + {X86_FEATURE_XMM2 ,X86_FEATURE_SSSE3 }, + {X86_FEATURE_XMM2 ,X86_FEATURE_F16C }, + {X86_FEATURE_XMM2 ,X86_FEATURE_AES }, + {X86_FEATURE_FMA ,X86_FEATURE_AVX }, + {X86_FEATURE_AVX512F ,X86_FEATURE_AVX512IFMA }, + {X86_FEATURE_AVX512F ,X86_FEATURE_AVX512PF }, + {X86_FEATURE_AVX512F ,X86_FEATURE_AVX512ER }, + {X86_FEATURE_AVX512F ,X86_FEATURE_AVX512CD }, + {X86_FEATURE_AVX512F ,X86_FEATURE_AVX512DQ }, + {X86_FEATURE_AVX512F ,X86_FEATURE_AVX512BW },
arch/x86/kernel/cpu/cpuid-deps.c line 52
Quoted 10 lines
arch/x86/kernel/cpu/cpuid-deps.c new file +10
-0+ { X86_FEATURE_AVX512F, X86_FEATURE_AVX512VL }, + { X86_FEATURE_AVX512F, X86_FEATURE_AVX512VBMI }, + { X86_FEATURE_AVX512F, X86_FEATURE_AVX512_4VNNIW }, + { X86_FEATURE_AVX512F, X86_FEATURE_AVX512_4FMAPS }, + { X86_FEATURE_AVX512F, X86_FEATURE_AVX512_VPOPCNTDQ }, + { X86_FEATURE_AVX, X86_FEATURE_AVX2 }, + {} +}; + +static inline void clearfeat (struct cpuinfo_x86 *cpu,int feat)
What's wrong with giving this a readable name like clear_feature()? That function name is definitely not a feat.
*cpu is the worst argument name you could come up with. I was not paying attention when skimming the patch and assumed that the 'if (!cpu)' check tests for cpu == 0, aka boot cpu.
Also the feature argument wants to be unsigned int all over the place.
Quoted 14 lines
arch/x86/kernel/cpu/cpuid-deps.c new file +14
-0+{ +if (!cpu) +__setup_clear_cpu_cap (feat); +else +__clear_cpu_cap (cpu, feat); +} + +static void do_clear_cpu_cap (struct cpuinfo_x86 *cpu,int feat) +{ +bool changed; +__u32 disable[NCAPINTS +NBUGINTS ]; +unsigned long *disable_mask = (unsigned long *)disable; +const struct cpuid_dep *d; +
arch/x86/kernel/cpu/cpuid-deps.c line 76
Quoted 10 lines
arch/x86/kernel/cpu/cpuid-deps.c new file +10
-0+clearfeat (cpu, feat); + +/* Collect all features to disable, handling dependencies */ +memset (disable,0 ,sizeof (disable)); +__set_bit (feat, disable_mask); + do { + changed = false; + for (d = cpuid_deps; d->feature; d++) { + if (test_bit(d->feature, disable_mask) && + !__test_and_set_bit(d->disable, disable_mask)) {
The logic of this dependency structure is backwards. As the name says its supposed to express dependencies. So it should actually do so:
struct cpuid_dep {
unsigned int feature;
unsigned int depends;
};Then the logic here becomes immediately obvious:
for (d = cpuid_deps; d->feature; d++) {
if (!test_bit(d->depends, disabled_mask))
continue;
if (test_and_set_bit(d->feature, disabled_mask))
continue;
changed = true;
clear_feature(cpuinfo, d->feature);
}Hmm?
Thanks,
tglx
PATCH v7 3/5 x86/cpuid: Make clearcpuid an early param
In reply to Andi KleenFrom: Andi Kleen <[email protected]>
Make clearcpuid= an early param, to make sure it is parsed before the XSAVE initialization. This allows to modify XSAVE state by clearing specific CPUID bits.
--- arch/x86/kernel/cpu/common.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
arch/x86/kernel/cpu/common.c +1 -1
@@ -1310,7 +1310,7 @@ static __init int setup_disablecpuid(char *arg)return 1 ; } -__setup ("clearcpuid=" , setup_disablecpuid); +early_param ("clearcpuid" , setup_disablecpuid);#ifdef CONFIG_X86_64 DEFINE_PER_CPU_FIRST(union irq_stack_union,
Signature · 1 line
2.13.6
Re: [PATCH v7 3/5] x86/cpuid: Make clearcpuid an early param
Quoted 7 lines · Andi Kleen
From: Andi Kleen <[email protected]>
Make clearcpuid= an early param, to make sure it is parsed before the XSAVE initialization. This allows to modify XSAVE state by clearing specific CPUID bits.
Signed-off-by Andi Kleen <[email protected]>
PATCH v7 4/5 x86/xsave: Make XSAVE check the base CPUID features before enabling
In reply to Andi KleenFrom: Andi Kleen <[email protected]>
Before enabling XSAVE, not only check the XSAVE specific CPUID bits, but also the base CPUID features of the respective XSAVE feature. This allows to disable individual XSAVE states using the existing clearcpuid= option, which can be useful for performance testing and debugging, and also in general avoids inconsistencies.
--- arch/x86/kernel/fpu/xstate.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)
arch/x86/kernel/fpu/xstate.c +22 -0
@@ -15,6 +15,7 @@#include <asm/fpu/xstate.h> #include <asm/tlbflush.h> +#include <asm/cpufeature.h> /* * Although we spell it out in here, the Processor Trace
@@ -36,6 +37,19 @@ static const char *xfeature_names[] = "unknown xstate feature" , }; +static short xsave_cpuid_features[] = { +X86_FEATURE_FPU , +X86_FEATURE_XMM , +X86_FEATURE_AVX , +X86_FEATURE_MPX , +X86_FEATURE_MPX , +X86_FEATURE_AVX512F , +X86_FEATURE_AVX512F , +X86_FEATURE_AVX512F , +X86_FEATURE_INTEL_PT , +X86_FEATURE_PKU , +}; +/* * Mask of xstate features supported by the CPU and the kernel: */
@@ -726,6 +740,7 @@ void __init fpu__init_system_xstate(void)unsigned int eax, ebx, ecx, edx;static int on_boot_cpu__initdata =1 ;int err; +int i;WARN_ON_FPU (!on_boot_cpu); on_boot_cpu =0 ;
@@ -759,6 +774,13 @@ void __init fpu__init_system_xstate(void) goto out_disable; } +/* +* Clear XSAVE features that are disabled in the normal CPUID. +*/ +for (i =0 ; i <ARRAY_SIZE (xsave_cpuid_features); i++) +if (!boot_cpu_has (xsave_cpuid_features[i])) + xfeatures_mask &= ~BIT (i); + xfeatures_mask &=fpu__get_supported_xfeatures_mask ();/* Enable xstate instructions to be able to continue with initialization: */
Signature · 1 line
2.13.6
Re: [PATCH v7 4/5] x86/xsave: Make XSAVE check the base CPUID features before enabling
arch/x86/kernel/fpu/xstate.c void __init fpu__init_system_xstate(void) · line 782
Quoted 6 lines · Andi Kleen
arch/x86/kernel/fpu/xstate.c +6
-0+/* +* Clear XSAVE features that are disabled in the normal CPUID. +*/ +for (i =0 ; i <ARRAY_SIZE (xsave_cpuid_features); i++) +if (!boot_cpu_has (xsave_cpuid_features[i])) + xfeatures_mask &= ~BIT (i);
Please add curly braces around this multi line statement.
https://marc.info/?l=linux-kernel&m=148467980905537&w=2
Thanks,
tglx
PATCH v7 5/5 x86/xsave: Using generic CPUID clearing when disabling XSAVE
In reply to Andi KleenFrom: Andi Kleen <[email protected]>
Now that the generic CPUID clearing understands dependencies, it's enough to clear the XSAVE CPUID bit to clear all depending features when XSAVE gets disabled.
So we don't need this hard to maintain explicit list of features depending on XSAVE anymore. Just call the generic clear_cpu_cap() function for XSAVE.
--- arch/x86/kernel/fpu/xstate.c | 20 -------------------- 1 file changed, 20 deletions(-)
arch/x86/kernel/fpu/xstate.c +0 -20
@@ -73,26 +73,6 @@ unsigned int fpu_user_xstate_size;void fpu__xstate_clear_all_cpu_caps (void ) {setup_clear_cpu_cap (X86_FEATURE_XSAVE ); -setup_clear_cpu_cap (X86_FEATURE_XSAVEOPT ); -setup_clear_cpu_cap (X86_FEATURE_XSAVEC ); -setup_clear_cpu_cap (X86_FEATURE_XSAVES ); -setup_clear_cpu_cap (X86_FEATURE_AVX ); -setup_clear_cpu_cap (X86_FEATURE_AVX2 ); -setup_clear_cpu_cap (X86_FEATURE_AVX512F ); -setup_clear_cpu_cap (X86_FEATURE_AVX512IFMA ); -setup_clear_cpu_cap (X86_FEATURE_AVX512PF ); -setup_clear_cpu_cap (X86_FEATURE_AVX512ER ); -setup_clear_cpu_cap (X86_FEATURE_AVX512CD ); -setup_clear_cpu_cap (X86_FEATURE_AVX512DQ ); -setup_clear_cpu_cap (X86_FEATURE_AVX512BW ); -setup_clear_cpu_cap (X86_FEATURE_AVX512VL ); -setup_clear_cpu_cap (X86_FEATURE_MPX ); -setup_clear_cpu_cap (X86_FEATURE_XGETBV1 ); -setup_clear_cpu_cap (X86_FEATURE_AVX512VBMI ); -setup_clear_cpu_cap (X86_FEATURE_PKU ); -setup_clear_cpu_cap (X86_FEATURE_AVX512_4VNNIW ); -setup_clear_cpu_cap (X86_FEATURE_AVX512_4FMAPS ); -setup_clear_cpu_cap (X86_FEATURE_AVX512_VPOPCNTDQ ); }/*
Signature · 1 line
2.13.6
Re: [PATCH v7 5/5] x86/xsave: Using generic CPUID clearing when disabling XSAVE
Quoted 9 lines · Andi Kleen
From: Andi Kleen <[email protected]>
Now that the generic CPUID clearing understands dependencies, it's enough to clear the XSAVE CPUID bit to clear all depending features when XSAVE gets disabled.
So we don't need this hard to maintain explicit list of features depending on XSAVE anymore. Just call the generic
clear_cpu_cap()function for XSAVE.
This changelog is hard to read and uses terms like 'CPUID clearing'. I know what you want to say, but this is far from being precise and understandable.
Aside of that the changelog violates as usual the changelog guidelines in Documentation/....
Something like this would be clear and precise:
Clearing a CPU feature with setup_clear_cpu_cap() clears all features which depend on it. Expressing feature dependencies in one place is easier to maintain than keeping functions like fpu__xstate_clear_all_cpu_caps() up to date.
The features which depend on XSAVE have their dependency expressed in the dependency table, so its sufficient to clear X86_FEATURE_XSAVE.
Remove the explicit clearing of XSAVE dependend features.
Hmm?
For the code patch itself:
Thanks,
tglx