From: Wanpeng Li wanpengli@tencent.com

The idea before commit 240c35a37 was that we have the following FPU states:

userspace (QEMU) guest --------------------------------------------------------------------------- processor vcpu->arch.guest_fpu

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KVM_RUN: kvm_load_guest_fpu

vcpu->arch.user_fpu processor

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preempt out

vcpu->arch.user_fpu current->thread.fpu

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preempt in

vcpu->arch.user_fpu processor

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back to userspace kvm_put_guest_fpu

processor vcpu->arch.guest_fpu ---------------------------------------------------------------------------

With the new lazy model we want to get the state back to the processor when schedule in from current->thread.fpu.

Reported-by: Thomas Lambertz mail@thomaslambertz.de Reported-by: anthony antdev66@gmail.com Tested-by: anthony antdev66@gmail.com Cc: Paolo Bonzini pbonzini@redhat.com Cc: Radim Krčmář rkrcmar@redhat.com Cc: Thomas Lambertz mail@thomaslambertz.de Cc: anthony antdev66@gmail.com Cc: stable@vger.kernel.org Fixes: 5f409e20b (x86/fpu: Defer FPU state load until return to userspace) Signed-off-by: Wanpeng Li wanpengli@tencent.com --- arch/x86/kvm/x86.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index cf2afdf..bdcd250 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3306,6 +3306,10 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)

kvm_x86_ops->vcpu_load(vcpu, cpu);

+ fpregs_assert_state_consistent(); + if (test_thread_flag(TIF_NEED_FPU_LOAD)) + switch_fpu_return(); + /* Apply any externally detected TSC adjustments (due to suspend) */ if (unlikely(vcpu->arch.tsc_offset_adjustment)) { adjust_tsc_offset_host(vcpu, vcpu->arch.tsc_offset_adjustment); @@ -7990,9 +7994,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) trace_kvm_entry(vcpu->vcpu_id); guest_enter_irqoff();

- fpregs_assert_state_consistent(); - if (test_thread_flag(TIF_NEED_FPU_LOAD)) - switch_fpu_return(); + WARN_ON_ONCE(test_thread_flag(TIF_NEED_FPU_LOAD));

if (unlikely(vcpu->arch.switch_db_regs)) { set_debugreg(0, 7);