Commit 95145c25 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86: Add a WARN on TIF_NEED_FPU_LOAD in kvm_load_guest_fpu() 



WARN once in kvm_load_guest_fpu() if TIF_NEED_FPU_LOAD is observed, as
that would mean that KVM is corrupting userspace's FPU by saving
unknown register state into arch.user_fpu.  Add a comment to explain
why KVM WARNs on TIF_NEED_FPU_LOAD instead of implementing logic
similar to fpu__copy().

Signed-off-by: default avatarSean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent f958bd23

arch/x86/kvm/x86.c

+7 −0
Original line number Diff line number Diff line
@@ -8476,6 +8476,13 @@ static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu) 
{

	fpregs_lock();



	/*

	 * Reloading userspace's FPU is handled by kvm_arch_vcpu_load(), both

	 * for direct calls from userspace (via vcpu_load()) and if this task

	 * is preempted (via kvm_sched_in()) between vcpu_load() and now.

	 */

	WARN_ON_ONCE(test_thread_flag(TIF_NEED_FPU_LOAD));



	copy_fpregs_to_fpstate(vcpu->arch.user_fpu);

	/* PKRU is separately restored in kvm_x86_ops->run.  */

	__copy_kernel_to_fpregs(&vcpu->arch.guest_fpu->state,