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SubjectRe: WARNING in switch_fpu_return
On Sun, Mar 22, 2020 at 03:41:03PM -0700, syzbot wrote:
> syzbot suspects this bug was fixed by commit:
>
> commit 3009afc6e39e78708d8fb444ae50544b3bcd3a3f
> Author: Sean Christopherson <sean.j.christopherson@intel.com>
> Date: Wed Jan 22 04:43:39 2020 +0000
>
> KVM: x86: Use a typedef for fastop functions
>
> bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1667aa4be00000
> start commit: bf8d1cd4 Merge tag 'scsi-fixes' of git://git.kernel.org/pu..
> git tree: upstream
> kernel config: https://syzkaller.appspot.com/x/.config?x=ed9d672709340e35
> dashboard link: https://syzkaller.appspot.com/bug?extid=f2ca20d4aa1408b0385a
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=151d549ee00000
>
> If the result looks correct, please mark the bug fixed by replying with:
>
> #syz fix: KVM: x86: Use a typedef for fastop functions

Ha, fat chance of that.

The offending call to switch_fpu_return() in kvm_arch_vcpu_load() was
removed by commit 2620fe268e80 ("KVM: x86: Revert "KVM: X86: Fix fpu state
crash in kvm guest"")

RIP: 0010:__fpregs_load_activate arch/x86/include/asm/fpu/internal.h:539 [inline]
RIP: 0010:switch_fpu_return+0x437/0x4f0 arch/x86/kernel/fpu/core.c:343
kvm_arch_vcpu_load+0x66e/0x950 arch/x86/kvm/x86.c:3463
vcpu_load+0x43/0x90 arch/x86/kvm/../../../virt/kvm/kvm_main.c:201
kvm_unload_vcpu_mmu arch/x86/kvm/x86.c:9543 [inline]
kvm_free_vcpus arch/x86/kvm/x86.c:9558 [inline]
kvm_arch_destroy_vm+0x184/0x5f0 arch/x86/kvm/x86.c:9663
kvm_destroy_vm arch/x86/kvm/../../../virt/kvm/kvm_main.c:816 [inline]
kvm_put_kvm+0x5a5/0xcc0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:837
async_pf_execute+0x3bf/0x800 arch/x86/kvm/../../../virt/kvm/async_pf.c:101
process_one_work+0x9af/0x1740 kernel/workqueue.c:2264
worker_thread+0x98/0xe40 kernel/workqueue.c:2410
kthread+0x361/0x430 kernel/kthread.c:255
ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352

So

#syz fix: KVM: x86: Revert "KVM: X86: Fix fpu state crash in kvm guest"

> For information about bisection process see: https://goo.gl/tpsmEJ#bisection

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