On 10.12.2017 22:44, Wanpeng Li wrote:
> From: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
>
> ------------[ 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@xxxxxxxxxx>
> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx>
> Cc: Rik van Riel <riel@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: f775b13eedee (x86,kvm: move qemu/guest FPU switching out to vcpu_run)
> Signed-off-by: Wanpeng Li <wanpeng.li@xxxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> 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 = ¤t->thread.fpu;
> + struct fpu *fpu = &vcpu->arch.user_fpu;
> int r;
>
> - fpu__initialize(fpu);
> + if (!fpu->initialized) {
> + fpstate_init(&fpu->state);
> + fpu->initialized = 1;
> + }
Is there a chance of keeping using fpu__initialize() ? Duplicating the
code is ugly.
E.g. can't we simply initialize that in kvm_load_guest_fpu?
>
> kvm_sigset_activate(vcpu);
>
>
--
Thanks,
David / dhildenb