From 95145c25a78cc0a9d3cbc75708abde432310c5a1 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Mon, 9 Dec 2019 12:05:17 -0800 Subject: [PATCH] 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: Sean Christopherson Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 0af5cb637bea..25aac4c81b12 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -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,