Re: [patch 13/31] x86/fpu: Move KVMs FPU swapping to FPU core

Borislav Petkov
2021-10-12T16:53:42Z

Just typos:

On Tue, Oct 12, 2021 at 02:00:17AM +0200, Thomas Gleixner wrote:
> Swapping the host/guest FPU is directly fiddling with FPU internals which
> requires 5 exports. The upcoming support of dymanically enabled states

"dynamically"

> /*
> * Use kernel_fpu_begin/end() if you intend to use FPU in kernel context. It
> * disables preemption so be careful if you intend to use it for long periods
> @@ -108,4 +110,10 @@ extern int cpu_has_xfeatures(u64 xfeatur
>
> static inline void update_pasid(void) { }
>
> +/* FPSTATE related functions which are exported to KVM */

fpstate-related

> +extern void fpu_init_fpstate_user(struct fpu *fpu);
> +
> +/* KVM specific functions */
> +extern void fpu_swap_kvm_fpu(struct fpu *save, struct fpu *rstor, u64 restore_mask);
> +
> #endif /* _ASM_X86_FPU_API_H */

...

> /* Swap (qemu) user FPU context for the guest FPU context. */
> static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
> {
> - fpregs_lock();
> -
> - kvm_save_current_fpu(vcpu->arch.user_fpu);
> -
> /*
> - * Guests with protected state can't have it set by the hypervisor,
> - * so skip trying to set it.
> + * Guest with protected state have guest_fpu == NULL which makes

"Guests ... "

> + * the swap only safe the host state. Exclude PKRU from restore as

"save"

> + * it is restored separately in kvm_x86_ops.run().
> */
> - if (vcpu->arch.guest_fpu)
> - /* PKRU is separately restored in kvm_x86_ops.run. */
> - __restore_fpregs_from_fpstate(&vcpu->arch.guest_fpu->state,
> - ~XFEATURE_MASK_PKRU);
> -
> - fpregs_mark_activate();
> - fpregs_unlock();
> -
> + fpu_swap_kvm_fpu(vcpu->arch.user_fpu, vcpu->arch.guest_fpu,
> + ~XFEATURE_MASK_PKRU);
> trace_kvm_fpu(1);
> }
>
> /* When vcpu_run ends, restore user space FPU context. */
> static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
> {
> - fpregs_lock();
> -
> /*
> - * Guests with protected state can't have it read by the hypervisor,
> - * so skip trying to save it.
> + * Guest with protected state have guest_fpu == NULL which makes

"Guests ... "

> + * swap only restore the host state.
> */
> - if (vcpu->arch.guest_fpu)
> - kvm_save_current_fpu(vcpu->arch.guest_fpu);
> -
> - restore_fpregs_from_fpstate(&vcpu->arch.user_fpu->state);
> -
> - fpregs_mark_activate();
> - fpregs_unlock();
> -
> + fpu_swap_kvm_fpu(vcpu->arch.guest_fpu, vcpu->arch.user_fpu, ~0ULL);
> ++vcpu->stat.fpu_reload;
> trace_kvm_fpu(0);
> }
> --- a/arch/x86/mm/extable.c
> +++ b/arch/x86/mm/extable.c
> @@ -47,7 +47,7 @@ static bool ex_handler_fprestore(const s
> WARN_ONCE(1, "Bad FPU state detected at %pB, reinitializing FPU registers.",
> (void *)instruction_pointer(regs));
>
> - __restore_fpregs_from_fpstate(&init_fpstate, xfeatures_mask_fpstate());
> + restore_fpregs_from_fpstate(&init_fpstate, xfeatures_mask_fpstate());
> return true;
> }
>
>

--
Regards/Gruss,
Boris.