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SubjectRe: [PATCH RFC 3/7] kvm: x86: XSAVE state and XFD MSRs context switch
Date
On 07/02/21 16:42, Jing Liu wrote:
> |In KVM, "guest_fpu" serves for any guest task working on this vcpu
> during vmexit and vmenter. We provide a pre-allocated guest_fpu space
> and entire "guest_fpu.state_mask" to avoid each dynamic features
> detection on each vcpu task. Meanwhile, to ensure correctly
> xsaves/xrstors guest state, set IA32_XFD as zero during vmexit and vmenter.|

Most guests will not need the whole xstate feature set. So perhaps you
could set XFD to the host value | the guest value, trap #NM if the
host XFD is zero, and possibly reflect the exception to the guest's XFD
and XFD_ERR.

In addition, loading the guest XFD MSRs should use the MSR autoload
feature (add_atomic_switch_msr).

Paolo

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