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Subject[PATCH 1/2] KVM: X86: Fix fpu state crash in kvm guest
Date
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
>>> KVM_RUN: kvm_load_guest_fpu
vcpu->arch.user_fpu processor
>>> preempt out
vcpu->arch.user_fpu current->thread.fpu
>>> preempt in
vcpu->arch.user_fpu processor
>>> 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);
--
2.7.4
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