On 27/12/2017 16:09, gregkh@linuxfoundation.org wrote:

The patch below does not apply to the 4.14-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

The code is new in 4.15.

Paolo

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 5663d8f9bbe4bf15488f7351efb61ea20fa6de06 Mon Sep 17 00:00:00 2001 From: Peter Xu peterx@redhat.com Date: Tue, 12 Dec 2017 17:15:02 +0100 Subject: [PATCH] kvm: x86: fix WARN due to uninitialized guest FPU state

------------[ 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

where kvm_put_guest_fpu is called without a prior kvm_load_guest_fpu. To fix it, move kvm_load_guest_fpu to the very beginning of kvm_arch_vcpu_ioctl_run.

Cc: stable@vger.kernel.org Fixes: f775b13eedee2f7f3c6fdd4e90fb79090ce5d339 Signed-off-by: Peter Xu peterx@redhat.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 154ea27746e9..56d036b9ad75 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -7264,13 +7264,12 @@ 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);

• kvm_load_guest_fpu(vcpu);
• if (unlikely(vcpu->arch.mp_state == KVM_MP_STATE_UNINITIALIZED)) { if (kvm_run->immediate_exit) { r = -EINTR;

@@ -7296,14 +7295,12 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) } }

• kvm_load_guest_fpu(vcpu);
• if (unlikely(vcpu->arch.complete_userspace_io)) { int (*cui)(struct kvm_vcpu *) = vcpu->arch.complete_userspace_io; vcpu->arch.complete_userspace_io = NULL; r = cui(vcpu); if (r <= 0)

• 	goto out_fpu;
  

• 	goto out;
  

  } else WARN_ON(vcpu->arch.pio.count || vcpu->mmio_needed);

@@ -7312,9 +7309,8 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run) else r = vcpu_run(vcpu); -out_fpu:

• kvm_put_guest_fpu(vcpu);

out:

• kvm_put_guest_fpu(vcpu); post_kvm_run_save(vcpu); kvm_sigset_deactivate(vcpu);