Re: [PATCH v3 7/8] KVM:X86: Add XSS bit 11 and 12 support for CET xsaves/xrstors.

From: Paolo Bonzini
Date: Fri Mar 08 2019 - 06:32:14 EST


On 28/02/19 09:44, Yang Weijiang wrote:
>>> if (!vmx_xsaves_supported())
>>> return 1;
>>> +
>>> /*
>>> - * The only supported bit as of Skylake is bit 8, but
>>> - * it is not supported on KVM.
>>> + * Check bits being set are supported in KVM.
>> I'd drop the comment altogether, it's pretty obvious from the code that
>> were checking which bits are supported.
> you won't see these redundancies in next version ;)
>>> */
>>> - if (data != 0)
>>> + if (data & ~kvm_supported_xss())
>>> return 1;

You should instead check this against CPUID[0xD, 1].EDX:ECX. If CET is
disabled in CPUID, the guest should not be able to set it in MSR_IA32_CSS.

Paolo