Re: [PATCH] KVM: x86: workaround invalid CPUID[0xD,9] info on some AMD processors

[Yang Zhong <yang.zhong@intel.com>]

On Wed, Mar 23, 2022 at 12:43:15PM +0100, Paolo Bonzini wrote:
> Some AMD processors expose the PKRU extended save state even if they do not have
> the related PKU feature in CPUID.  Worse, when they do they report a size of
> 64, whereas the expected size of the PKRU extended save state is 8, therefore
> the esa->size == eax assertion does not hold.
> 
> The state is already ignored by KVM_GET_SUPPORTED_CPUID because it
> was not enabled in the host XCR0.  However, QEMU kvm_cpu_xsave_init()
> runs before QEMU invokes arch_prctl() to enable dynamically-enabled
> save states such as XTILEDATA, and KVM_GET_SUPPORTED_CPUID hides save
> states that have yet to be enabled.  Therefore, kvm_cpu_xsave_init()
> needs to consult the host CPUID instead of KVM_GET_SUPPORTED_CPUID,
> and dies with an assertion failure.
> 
> When setting up the ExtSaveArea array to match the host, ignore features that
> KVM does not report as supported.  This will cause QEMU to skip the incorrect
> CPUID leaf instead of tripping the assertion.
> 
> Reported-by: Daniel P. Berrangé <berrange@redhat.com>
> Analyzed-by: Yang Zhong <yang.zhong@intel.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  target/i386/cpu.c         |  4 ++--
>  target/i386/cpu.h         |  2 ++
>  target/i386/kvm/kvm-cpu.c | 19 ++++++++++++-------
>  3 files changed, 16 insertions(+), 9 deletions(-)

   Verified this patch on AMD EPYC 7402P, no crash issue now. thanks!

   Yang