Re: [PATCH v1 3/9] target/i386: Hide ARCH_CAPABILITIES for Hygon

On Mon, Jul 06, 2026 at 01:55:24PM +0800, [email protected] wrote:
> Date: Mon,  6 Jul 2026 13:55:24 +0800
> From: [email protected]
> Subject: [PATCH v1 3/9] target/i386: Hide ARCH_CAPABILITIES for Hygon
> X-Mailer: git-send-email 2.43.7
> 
> From: Tina Zhang <[email protected]>
> 
> IA32_ARCH_CAPABILITIES is an Intel-defined MSR.  KVM can synthesize the
> CPUID bit and read-only MSR for non-Intel guests, and QEMU already hides
> that interface for AMD CPU models because Windows may not expect it on
> AMD-compatible CPUs.
> 
> Hygon Dhyana uses the HygonGenuine vendor string, so it currently skips
> that AMD filter.  If arch-capabilities=on is requested, QEMU can expose
> CPUID.7.0.EDX[ARCH_CAPABILITIES] and the associated MSR feature word to
> a Hygon guest.
> 
> That creates a vendor-inconsistent CPU ABI: the guest sees an
> AMD-compatible vendor and cache/topology interface, but also sees an
> Intel-specific architectural capabilities MSR.  Guests that choose CPU
> mitigation or feature paths from the vendor can mis-handle that
> combination; Windows is known to be sensitive to ARCH_CAPABILITIES on
> AMD-compatible CPUs.
> 
> Apply the same ARCH_CAPABILITIES hiding rule to Hygon CPUs when Hygon
> vendor ABI fixes are enabled.  Keep arch_cap_always_on as the migration
> escape hatch, and keep the old Hygon CPUID/MSR output for pc-11.0 and
> older machine types via x-hygon-vendor-abi-fixes=false.
> 
> Signed-off-by: Tina Zhang <[email protected]>
> ---
>  target/i386/cpu.c | 33 ++++++++++++++++++++++++---------
>  1 file changed, 24 insertions(+), 9 deletions(-)

Reviewed-by: Zhao Liu <[email protected]>