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    SubjectRe: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core
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    On 13/10/21 08:15, Liu, Jing2 wrote:
    > After KVM passthrough XFD to guest, when vmexit opening
    > irq window and KVM is interrupted, kernel softirq path can call
    > kernel_fpu_begin() to touch xsave state. This function does
    > XSAVES. If guest XFD[18] is 1, and with guest AMX state in register,
    > then guest AMX state is lost by XSAVES.

    Yes, the host value of XFD (which is zero) has to be restored after
    vmexit. See how KVM already handles SPEC_CTRL.

    Passthrough of XFD is only enabled after the guest has caused an #NM
    vmexit and the full XSAVE state has been dynamically allocated,
    therefore it is always possible to do an XSAVES even from atomic context.

    Paolo

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