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KVM: X86: Fix load bad host fpu state

Message ID 1512941634-40254-1-git-send-email-wanpeng.li@hotmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Wanpeng Li Dec. 10, 2017, 9:33 p.m. UTC 
From: Wanpeng Li <wanpeng.li@hotmail.com>

------------[ cut here ]------------
 Bad FPU state detected at kvm_put_guest_fpu+0xd8/0x2d0 [kvm], reinitializing FPU registers.
 WARNING: CPU: 1 PID: 4594 at arch/x86/mm/extable.c:103 ex_handler_fprestore+0x88/0x90
 CPU: 1 PID: 4594 Comm: qemu-system-x86 Tainted: G    B      OE    4.15.0-rc2+ #10
 RIP: 0010:ex_handler_fprestore+0x88/0x90
 Call Trace:
  fixup_exception+0x4e/0x60
  do_general_protection+0xff/0x270
  general_protection+0x22/0x30
 RIP: 0010:kvm_put_guest_fpu+0xd8/0x2d0 [kvm]
 RSP: 0018:ffff8803d5627810 EFLAGS: 00010246
  kvm_vcpu_reset+0x3b4/0x3c0 [kvm]
  kvm_apic_accept_events+0x1c0/0x240 [kvm]
  kvm_arch_vcpu_ioctl_run+0x1658/0x2fb0 [kvm]
  kvm_vcpu_ioctl+0x479/0x880 [kvm]
  do_vfs_ioctl+0x142/0x9a0
  SyS_ioctl+0x74/0x80
  do_syscall_64+0x15f/0x600

This can be reproduced by running any testcase in kvm-unit-tests since 
the qemu userspace FPU context is not initialized, which results in the 
init path from kvm_apic_accept_events() will load/put qemu userspace 
FPU context w/o initialized. In addition, w/o this splatting we still 
should initialize vcpu->arch.user_fpu instead of current->thread.fpu. 
This patch fixes it by initializing qemu user FPU context if it is 
uninitialized before KVM_RUN.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: stable@vger.kernel.org
Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 arch/x86/kvm/x86.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
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Patch

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a92b22f..063a643 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7273,10 +7273,13 @@  static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
 
 int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
 {
-	struct fpu *fpu = &current->thread.fpu;
+	struct fpu *fpu = &vcpu->arch.user_fpu;
 	int r;
 
-	fpu__initialize(fpu);
+	if (!fpu->initialized) {
+		fpstate_init(&vcpu->arch.user_fpu.state);
+		fpu->initialized = 1;
+	}
 
 	kvm_sigset_activate(vcpu);