On 27/12/2017 16:09, gregkh@xxxxxxxxxxxxxxxxxxx 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@xxxxxxxxxxxxxxx>.
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@xxxxxxxxxx>
> 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@xxxxxxxxxxxxxxx
> Fixes: f775b13eedee2f7f3c6fdd4e90fb79090ce5d339
> Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
>
> 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 = ¤t->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);
>
>