Re: [PATCH 1/4] x86/fpu: Clear XSTATE_BV[i] in save state whenever XFD[i]=1

[Dave Hansen]

On 1/1/26 01:05, Paolo Bonzini wrote:
> When loading guest XSAVE state via KVM_SET_XSAVE, and when updating XFD in
> response to a guest WRMSR, clear XFD-disabled features in the saved (or to
> be restored) XSTATE_BV to ensure KVM doesn't attempt to load state for
> features that are disabled via the guest's XFD.  Because the kernel
> executes XRSTOR with the guest's XFD, saving XSTATE_BV[i]=1 with XFD[i]=1
> will cause XRSTOR to #NM and panic the kernel.

It would be really nice to see the actual ordering of events here. What
order do the KVM_SET_XSAVE, XFD[$FOO]=1 and kernel_fpu_begin() have to
happen in to trigger this?