| Message ID | 20220901211811.2883855-1-jmattson@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3,1/2] x86/cpufeatures: Add macros for Intel's new fast rep string features | expand |
On 9/1/22 14:18, Jim Mattson wrote: > KVM_GET_SUPPORTED_CPUID should reflect these host CPUID bits. The bits > are already cached in word 12. Give the bits X86_FEATURE names, so > that they can be easily referenced. Hide these bits from > /proc/cpuinfo, since the host kernel makes no use of them at present. > > Signed-off-by: Jim Mattson <jmattson@google.com> > --- > arch/x86/include/asm/cpufeatures.h | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h > index ef4775c6db01..454f0faa8e90 100644 > --- a/arch/x86/include/asm/cpufeatures.h > +++ b/arch/x86/include/asm/cpufeatures.h > @@ -308,6 +308,9 @@ > /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */ > #define X86_FEATURE_AVX_VNNI (12*32+ 4) /* AVX VNNI instructions */ > #define X86_FEATURE_AVX512_BF16 (12*32+ 5) /* AVX512 BFLOAT16 instructions */ > +#define X86_FEATURE_FZRM (12*32+10) /* "" Fast zero-length REP MOVSB */ > +#define X86_FEATURE_FSRS (12*32+11) /* "" Fast short REP STOSB */ > +#define X86_FEATURE_FSRC (12*32+12) /* "" Fast short REP {CMPSB,SCASB} */ > > /* AMD-defined CPU features, CPUID level 0x80000008 (EBX), word 13 */ > #define X86_FEATURE_CLZERO (13*32+ 0) /* CLZERO instruction */ Any reason why these bits are hidden from /proc/cpuinfo? -hpa
On Thu, Sep 01, 2022 at 09:14:24PM -0700, H. Peter Anvin wrote:
> Any reason why these bits are hidden from /proc/cpuinfo?
Yes, we aim to hide such purely CPUID bits from /proc/cpuinfo because it
becomes a dumping ground for "enablement" of new features. But
1. those features are not really used - most userspace like binutils and
gcc, etc do their own detection. (Yes, yes, I'd like to have ubiquitous
CPUID faulting).
2. /proc/cpuinfo is an ABI so we have to carry *all* those gazillion
flags for no good reason
So we have tools/arch/x86/kcpuid/ which we control and we can extend
with all the CPUID querying needs we have.
These kvm enablement things are kinda needed because guest userspace
gets an emulated CPUID so in order to detect features on its own, it
needs them. And kvm has tied features to x86's X86_FEATURE stuff and
there are sometimes weird interactions with it too but that's another
topic...
Oh and we still do add visible flags to /proc/cpuinfo but only when
they're features which need and have received non-trivial kernel
enablement like TDX or SNP or so.
On Thu, Sep 01, 2022, Jim Mattson wrote: > KVM_GET_SUPPORTED_CPUID should reflect these host CPUID bits. The bits > are already cached in word 12. Give the bits X86_FEATURE names, so > that they can be easily referenced. Hide these bits from > /proc/cpuinfo, since the host kernel makes no use of them at present. > > Signed-off-by: Jim Mattson <jmattson@google.com> > --- Reviewed-by: Sean Christopherson <seanjc@google.com>
On Thu, 01 Sep 2022 14:18:06 -0700, Jim Mattson wrote: > KVM_GET_SUPPORTED_CPUID should reflect these host CPUID bits. The bits > are already cached in word 12. Give the bits X86_FEATURE names, so > that they can be easily referenced. Hide these bits from > /proc/cpuinfo, since the host kernel makes no use of them at present. > > Applied to kvm-x86 misc, thanks! [1/2] x86/cpufeatures: Add macros for Intel's new fast rep string features https://github.com/kvm-x86/linux/commit/751b1e1ee8e9 [2/2] KVM: x86: Expose CPUID.(EAX=7,ECX=1).EAX[12:10] to the guest https://github.com/kvm-x86/linux/commit/bbbe171ac12f -- https://github.com/kvm-x86/linux/tree/next https://github.com/kvm-x86/linux/tree/fixes
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h index ef4775c6db01..454f0faa8e90 100644 --- a/arch/x86/include/asm/cpufeatures.h +++ b/arch/x86/include/asm/cpufeatures.h @@ -308,6 +308,9 @@ /* Intel-defined CPU features, CPUID level 0x00000007:1 (EAX), word 12 */ #define X86_FEATURE_AVX_VNNI (12*32+ 4) /* AVX VNNI instructions */ #define X86_FEATURE_AVX512_BF16 (12*32+ 5) /* AVX512 BFLOAT16 instructions */ +#define X86_FEATURE_FZRM (12*32+10) /* "" Fast zero-length REP MOVSB */ +#define X86_FEATURE_FSRS (12*32+11) /* "" Fast short REP STOSB */ +#define X86_FEATURE_FSRC (12*32+12) /* "" Fast short REP {CMPSB,SCASB} */ /* AMD-defined CPU features, CPUID level 0x80000008 (EBX), word 13 */ #define X86_FEATURE_CLZERO (13*32+ 0) /* CLZERO instruction */
KVM_GET_SUPPORTED_CPUID should reflect these host CPUID bits. The bits are already cached in word 12. Give the bits X86_FEATURE names, so that they can be easily referenced. Hide these bits from /proc/cpuinfo, since the host kernel makes no use of them at present. Signed-off-by: Jim Mattson <jmattson@google.com> --- arch/x86/include/asm/cpufeatures.h | 3 +++ 1 file changed, 3 insertions(+)