Re: [PATCH 10/19] kvm: x86: Emulate WRMSR of guest IA32_XFD

Thomas Gleixner
2021-12-13T19:45:56Z

On Mon, Dec 13 2021 at 16:06, Paolo Bonzini wrote:
> On 12/8/21 01:03, Yang Zhong wrote:
>> + /*
>> + * Update IA32_XFD to the guest value so #NM can be
>> + * raised properly in the guest. Instead of directly
>> + * writing the MSR, call a helper to avoid breaking
>> + * per-cpu cached value in fpu core.
>> + */
>> + fpregs_lock();
>> + current->thread.fpu.fpstate->xfd = data;
>
> This is wrong, it should be written in vcpu->arch.guest_fpu.
>
>> + xfd_update_state(current->thread.fpu.fpstate);
>
> This is okay though, so that KVM_SET_MSR will not write XFD and WRMSR
> will.
>
> That said, I think xfd_update_state should not have an argument.
> current->thread.fpu.fpstate->xfd is the only fpstate that should be
> synced with the xfd_state per-CPU variable.

I'm looking into this right now. The whole restore versus runtime thing
needs to be handled differently.

Thanks,

tglx