Re: [Qemu-devel] [PATCH v2 2/5] target/i386: Populate AMD Processor Cache Information

["Radim Krčmář" <rkrcmar@redhat.com>]

2018-03-01 15:55+0000, Moger, Babu:
> Radim, Thanks for your comments. I am working on the changes.
> But, I need few clarifications on your comments. Please see inline. 
> 
> > -----Original Message-----
> > From: Radim Krčmář [mailto:rkrcmar@redhat.com]
> > Sent: Wednesday, February 28, 2018 12:09 PM
> > To: Moger, Babu <Babu.Moger@amd.com>
> > Cc: pbonzini@redhat.com; rth@twiddle.net; ehabkost@redhat.com;
> > mtosatti@redhat.com; qemu-devel@nongnu.org; kvm@vger.kernel.org;
> > pixo@polepetko.eu; Hook, Gary <Gary.Hook@amd.com>
> > Subject: Re: [PATCH v2 2/5] target/i386: Populate AMD Processor Cache
> > Information
> > 
> > 2018-02-23 21:30-0500, Babu Moger:
> > > From: Stanislav Lanci <pixo@polepetko.eu>
> > >
> > > Adds information about cache size and topology from cpuid 0x8000001D
> > leaf
> > > for different cache types on AMD processors.
> > >
> > > Signed-off-by: Stanislav Lanci <pixo@polepetko.eu>
> > > Signed-off-by: Babu Moger <babu.moger@amd.com>
> > > ---
> > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > > @@ -3590,6 +3594,78 @@ void cpu_x86_cpuid(CPUX86State *env,
> > > +                *ebx = (L1D_LINE_SIZE - 1) | \
> > > +                       ((L1D_PARTITIONS - 1) << 12) | \
> > > +                       ((L1D_ASSOCIATIVITY - 1) << 22);
> > > +                *ecx = L1D_SETS - 1;
> > 
> > These numbers seem to have the same meaning as CPUID 4, but have
> > conflicting values.
> 
> I am not sure about conflicting values. Looking at the specs(page 78 CPUID_Fn8000001D_EBX_x00)
>  https://support.amd.com/TechDocs/54945_PPR_Family_17h_Models_00h-0Fh.pdf
>  It looks correct to me.

I agree.  My comment is misplaced -- it should have been under the place
that uses *_AMD macros.

I wanted to point out that CPUID in QEMU is very Intel-focused and
always contains CPUID leaf 4, which has fields of the very same meaning,
but with different values.

> > I think we should not expose CPUID 4 with AMD CPUs or at least when they
> > have CPUID_EXT3_TOPOEXT (the latter is easier wrt. compatibility).
> 
> Can you please elaborate on these comments? 
> Did you mean we should remove the check CPUID_EXT3_TOPOEXT and remove all CPUID 4 references? 

CPUID 4 should have never been present when emulating AMD CPUs, but it's
worse now that the numbers are conflicting.

I meant to hide CPUID 4 for all AMD CPUs on future machine types, or at
least when CPUID_EXT3_TOPOEXT is enabled.

Keeping the current logic not a big problem as CPUID 4 should never be
used by operating systems on AMD nor trusted inside a VM.  Bringing the
emulation closer to real state would be nice, but this can definitely be
done later (aka never).

> > The numbers looks like real hardware,
> 
> Do you want me to change anything here?

No, I was just commending,

thanks.