Re: [PATCH v1 7/8] kvm:cpuid Fix xsaves area size calculation for CPUID.(EAX=0xD,ECX=1).

Sean Christopherson
2019-01-02T18:54:56Z

On Wed, Dec 26, 2018 at 04:15:31PM +0800, Yang Weijiang wrote:
> According to latest Software Development Manual vol.2/3.2,
> for CPUID.(EAX=0xD,ECX=1), it should report xsaves area size
> containing all states enabled by XCR0|IA32_MSR_XSS.
>
> Signed-off-by: Zhang Yi Z <yi.z.zhang@linux.intel.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
> arch/x86/kvm/cpuid.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 5bac31e58955..55c282f71f93 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -121,7 +121,8 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>
> best = kvm_find_cpuid_entry(vcpu, 0xD, 1);
> if (best && (best->eax & (F(XSAVES) | F(XSAVEC))))
> - best->ebx = xstate_required_size(vcpu->arch.xcr0, true);
> + best->ebx = xstate_required_size(vcpu->arch.xcr0 |
> + best->ecx | ((u64)best->edx << 32), true);

Passing the CPUID bits is wrong, it needs to be the guest's IA32_MSR_XSS.
The CPUID bits enumerate what is legal to enable, not what features are
actually enabled by software.

>
> /*
> * The existing code assumes virtual address is 48-bit or 57-bit in the
> --
> 2.17.1
>