Messages in this thread | | | Date | Fri, 10 Dec 2021 17:16:47 +0100 | Subject | Re: [PATCH 14/19] x86/fpu: Prepare for KVM XFD_ERR handling | From | Paolo Bonzini <> |
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On 12/8/21 01:03, Yang Zhong wrote: > > The guest XFD_ERR value is saved in fpu_guest::xfd_err. There is > no need to save host XFD_ERR because it's always cleared to ZERO > by the host #NM handler (which cannot be preempted by a vCPU > thread to observe a non-zero value). > > The lower two bits in fpu_guest::xfd_err is borrowed for special > purposes. The state components (FP and SSE) covered by the two > bits are not XSAVE-enabled feature, thus not XFD-enabled either. > It's impossible to see hardware setting them in XFD_ERR: > > - XFD_ERR_GUEST_DISABLED (bit 0) > > Indicate that XFD extension is not exposed to the guest thus > no need to save/restore it.
Can this instead just check if xfeatures includes any dynamic-save features?
Paolo
> - XFD_ERR_GUEST_SAVED (bit 1) > > Indicate fpu_guest::xfd_err already contains a saved value > thus no need for duplicated saving (e.g. when the vCPU thread > is preempted multiple times before re-enter the guest).
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