On 12/12/2017 06:40, Wanpeng Li wrote:
2017-12-12 11:36 GMT+08:00 Peter Xu peterx@redhat.com:
On Tue, Dec 12, 2017 at 05:51:26AM +0800, Wanpeng Li wrote:
2017-12-12 4:48 GMT+08:00 David Hildenbrand david@redhat.com:
On 10.12.2017 22:44, Wanpeng Li wrote:
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(-)
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.
There is a warning in fpu__initialize() which results in just current->thread.fpu can take advantage of.
E.g. can't we simply initialize that in kvm_load_guest_fpu?
We still miss to initialize qemu user FPU context for the above calltrace.
IMHO we should not really init the user FPU since we should always load FPU then put FPU. The problem now is that for vcpus that with vcpu_id>1 we'll first put the FPU before loading it. So, instead how about we make sure we load the FPU first even for non-bootstrap vcpus? And we can actually drop fpu__initialize() call, like:
It will introduce extra overhead for all the cases which can't enter into vcpu_run(), I think move fpstate_init(&vcpu->arch.user_fpu.state); to fx_init() is better.
Those cases with a sleeping AP are so rare that they don't matter. They will occur only a few times per boot. Peter's solution is right, I've queued it.
Thanks to both!
Paolo
Paolo