Re: [PATCH 1/6] target/i386: Add AVX512 state when AVX10 is supported

[Tao Su <tao1.su@linux.intel.com>]

On Tue, Oct 29, 2024 at 09:49:39AM +0100, Paolo Bonzini wrote:
> On 10/28/24 10:25, Tao Su wrote:
> > On Mon, Oct 28, 2024 at 09:41:14AM +0100, Paolo Bonzini wrote:
> > > On 10/28/24 03:45, Tao Su wrote:
> > > > AVX10 state enumeration in CPUID leaf D and enabling in XCR0 register
> > > > are identical to AVX512 state regardless of the supported vector lengths.
> > > > 
> > > > Given that some E-cores will support AVX10 but not support AVX512, add
> > > > AVX512 state components to guest when AVX10 is enabled.
> > > > 
> > > > Tested-by: Xuelian Guo <xuelian.guo@intel.com>
> > > > Signed-off-by: Tao Su <tao1.su@linux.intel.com>
> > > > ---
> > > >    target/i386/cpu.c | 14 ++++++++++++++
> > > >    target/i386/cpu.h |  2 ++
> > > >    2 files changed, 16 insertions(+)
> > > > 
> > > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > > > index 1ff1af032e..d845ff5e4e 100644
> > > > --- a/target/i386/cpu.c
> > > > +++ b/target/i386/cpu.c
> > > > @@ -7177,6 +7177,13 @@ static void x86_cpu_reset_hold(Object *obj, ResetType type)
> > > >            }
> > > >            if (env->features[esa->feature] & esa->bits) {
> > > >                xcr0 |= 1ull << i;
> > > > +            continue;
> > > > +        }
> > > > +        if (i == XSTATE_OPMASK_BIT || i == XSTATE_ZMM_Hi256_BIT ||
> > > > +            i == XSTATE_Hi16_ZMM_BIT) {
> > > 
> > > Can you confirm that XSTATE_ZMM_Hi256_BIT depends on AVX10 and not
> > > AVX10-512?
> > > 
> > 
> > Sorry, I should attach AVX10.2 spec [*].
> > 
> > In 3.1.3, spec said Intel AVX10 state enumeration in CPUID leaf 0xD and
> > enabling in XCR0 register are identical to Intel AVX-512 regardless of the
> > maximum vector length supported.
> > 
> > So XSTATE_ZMM_Hi256_BIT doesn't depend on AVX10-512.
> > 
> > [*] https://cdrdv2.intel.com/v1/dl/getContent/828965
> 
> Ok, thanks.
> 
> Another related issue is that kvm_cpu_xsave_init() is using esa->feature and
> esa->bits, which misses these three features.

Yes, it has issue if AVX512F is not reported but AVX10 is reported, thanks for
pointing out!

> 
> I think we need to change the code to not look at esa->feature at all. I'll
> send a v2 of your series.
> 

Yes, ExtSaveArea can't set more feature bits, which makes the code a bit ugly.
Looking forward to the better implementation :-)