Re: [PATCH v2 3/9] target/i386: Hide ARCH_CAPABILITIES for Hygon

On Mon, Aug 10, 2026 at 04:29:50PM +0800, Tina Zhang wrote:
> Date: Mon, 10 Aug 2026 16:29:50 +0800
> From: Tina Zhang <[email protected]>
> Subject: [PATCH v2 3/9] target/i386: Hide ARCH_CAPABILITIES for Hygon
> X-Mailer: git-send-email 2.43.7
> 
> 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 the vendor
> CPU ABI compat gate is 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.

Nit: pc-11.1? Same applies to the other commit messages.

Thanks,
Zhao