Re: [PATCH v1] KVM: x86: expose AVX512_BF16 feature to guest

[Wanpeng Li <kernellwp@gmail.com>]

On Sat, 13 Jul 2019 at 18:40, Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 11/07/19 07:49, Jing Liu wrote:
> > AVX512 BFLOAT16 instructions support 16-bit BFLOAT16 floating-point
> > format (BF16) for deep learning optimization.
> >
> > Intel adds AVX512 BFLOAT16 feature in CooperLake, which is CPUID.7.1.EAX[5].
> >
> > Detailed information of the CPUID bit can be found here,
> > https://software.intel.com/sites/default/files/managed/c5/15/\
> > architecture-instruction-set-extensions-programming-reference.pdf.
> >
> > Signed-off-by: Jing Liu <jing2.liu@linux.intel.com>
> > ---
> >
> > This patch depends on kernel patch https://lkml.org/lkml/2019/6/19/912
> > and Paolo's patch set https://lkml.org/lkml/2019/7/4/468.
> >
> >  arch/x86/kvm/cpuid.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index 8fc6039..0c125dd 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -358,9 +358,13 @@ static inline void do_cpuid_7_mask(struct kvm_cpuid_entry2 *entry, int index)
> >               F(SPEC_CTRL_SSBD) | F(ARCH_CAPABILITIES) | F(INTEL_STIBP) |
> >               F(MD_CLEAR);
> >
> > +     /* cpuid 7.1.eax */
> > +     const u32 kvm_cpuid_7_1_eax_x86_features =
> > +             F(AVX512_BF16);
> > +
> >       switch (index) {
> >       case 0:
> > -             entry->eax = 0;
> > +             entry->eax = min(entry->eax, 1);
> >               entry->ebx &= kvm_cpuid_7_0_ebx_x86_features;
> >               cpuid_mask(&entry->ebx, CPUID_7_0_EBX);
> >               /* TSC_ADJUST is emulated */
> > @@ -384,6 +388,12 @@ static inline void do_cpuid_7_mask(struct kvm_cpuid_entry2 *entry, int index)
> >                */
> >               entry->edx |= F(ARCH_CAPABILITIES);
> >               break;
> > +     case 1:
> > +             entry->eax &= kvm_cpuid_7_1_eax_x86_features;
> > +             entry->ebx = 0;
> > +             entry->ecx = 0;
> > +             entry->edx = 0;
> > +             break;
> >       default:
> >               WARN_ON_ONCE(1);
> >               entry->eax = 0;
> >
>
> Queued, thanks.

I see this in kvm/queue:

In file included from ./include/linux/list.h:9:0,
                 from ./include/linux/preempt.h:11,
                 from ./include/linux/hardirq.h:5,
                 from ./include/linux/kvm_host.h:7,
                 from /home/kernel/data/kvm/arch/x86/kvm//cpuid.c:12:
/home/kernel/data/kvm/arch/x86/kvm//cpuid.c: In function ‘do_cpuid_7_mask’:
./include/linux/kernel.h:819:29: warning: comparison of distinct
pointer types lacks a cast
   (!!(sizeof((typeof(x) *)1 == (typeof(y) *)1)))
                             ^
./include/linux/kernel.h:833:4: note: in expansion of macro ‘__typecheck’
   (__typecheck(x, y) && __no_side_effects(x, y))
    ^
./include/linux/kernel.h:843:24: note: in expansion of macro ‘__safe_cmp’
  __builtin_choose_expr(__safe_cmp(x, y), \
                        ^
./include/linux/kernel.h:852:19: note: in expansion of macro ‘__careful_cmp’
 #define min(x, y) __careful_cmp(x, y, <)
                   ^
/home/kernel/data/kvm/arch/x86/kvm//cpuid.c:377:16: note: in expansion
of macro ‘min’
   entry->eax = min(entry->eax, 1);
                ^