Messages in this thread | | | Date | Wed, 13 Oct 2021 08:26:36 +0200 | Subject | Re: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core | From | Paolo Bonzini <> |
| |
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
| |