linux-kernel - [PATCH v2] KVM: X86: Fix load bad host fpu state

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Message-Id: <1513139666-10805-1-git-send-email-wanpeng.li@hotmail.com>
Date:   Tue, 12 Dec 2017 20:34:26 -0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpeng.li@...mail.com>,
        Rik van Riel <riel@...hat.com>
Subject: [PATCH v2] KVM: X86: Fix load bad host fpu state

From: Wanpeng Li <wanpeng.li@...mail.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 during vCPU 
creation.

Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Radim Krčmář <rkrcmar@...hat.com>
Cc: Rik van Riel <riel@...hat.com>
Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
---
v1 -> v2:
 * initialize user_fpu in fx_init

 arch/x86/kvm/x86.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5134a85..6a837fa 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7278,11 +7278,8 @@ 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;
 	int r;
 
-	fpu__initialize(fpu);
-
 	kvm_sigset_activate(vcpu);
 
 	if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) {
@@ -7709,6 +7706,7 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
 static void fx_init(struct kvm_vcpu *vcpu)
 {
 	fpstate_init(&vcpu->arch.guest_fpu.state);
+	fpstate_init(&vcpu->arch.user_fpu.state);
 	if (boot_cpu_has(X86_FEATURE_XSAVES))
 		vcpu->arch.guest_fpu.state.xsave.header.xcomp_bv =
 			host_xcr0 | XSTATE_COMPACTION_ENABLED;
-- 
2.7.4