linux-kernel - Re: WARNING in switch_fpu

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Message-ID: <20200323150107.GB28711@linux.intel.com>
Date:   Mon, 23 Mar 2020 08:01:08 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     syzbot <syzbot+f2ca20d4aa1408b0385a@...kaller.appspotmail.com>
Cc:     alexander.deucher@....com, bigeasy@...utronix.de, bp@...en8.de,
        dave.hansen@...el.com, dvyukov@...gle.com, hpa@...or.com,
        linmiaohe@...wei.com, linux-kernel@...r.kernel.org,
        mingo@...hat.com, nicholas.kazlauskas@....com, pbonzini@...hat.com,
        riel@...riel.com, sunpeng.li@....com,
        syzkaller-bugs@...glegroups.com, tglx@...utronix.de,
        x86@...nel.org, zhan.liu@....com
Subject: Re: 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@...el.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