Re: WARNING in try_grab_page

[Matthew Wilcox]

On Thu, Aug 03, 2023 at 04:56:03PM +0800, Yikebaer Aizezi wrote:
> console output:
> https://drive.google.com/file/d/1Lq71bFwtEDix82PEf_193CLG6uh1Pjj9/view?usp=drive_link
> kernel config: https://drive.google.com/file/d/1dApy7OR4KDYdhF96ZUowZQ1r-uLYTd-0/view?usp=drive_link
> C reproducer: https://drive.google.com/file/d/1Dkj31wwYP7p-AEJeemD3yrIUr7-VdBqF/view?usp=drive_link

Are you sure this is right?  The below stack trace shows something
coming in through the ioctl() path, but nothing in this reproducer
calls ioctl().  It's just socket(), bind(), accept4() and sendmsg().
I don't see a way to come up with this stack backtrace from that
program.

> Call Trace:
>  <TASK>
>  follow_page_pte+0x18c/0x1610 mm/gup.c:651
>  follow_pmd_mask mm/gup.c:727 [inline]
>  follow_pud_mask mm/gup.c:765 [inline]
>  follow_p4d_mask mm/gup.c:782 [inline]
>  follow_page_mask+0x2e4/0xbd0 mm/gup.c:839
>  __get_user_pages+0x3fa/0xcf0 mm/gup.c:1256
>  __get_user_pages_locked mm/gup.c:1487 [inline]
>  get_user_pages_unlocked+0x183/0x580 mm/gup.c:2387
>  hva_to_pfn_slow arch/x86/kvm/../../../virt/kvm/kvm_main.c:2536 [inline]
>  hva_to_pfn+0x198/0xbc0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2674
>  __gfn_to_pfn_memslot+0x202/0x3e0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:2736
>  __kvm_faultin_pfn arch/x86/kvm/mmu/mmu.c:4329 [inline]
>  kvm_faultin_pfn+0x21b/0x12d0 arch/x86/kvm/mmu/mmu.c:4365
>  kvm_tdp_mmu_page_fault arch/x86/kvm/mmu/mmu.c:4503 [inline]
>  kvm_tdp_page_fault+0x167/0x4d0 arch/x86/kvm/mmu/mmu.c:4549
>  kvm_mmu_do_page_fault arch/x86/kvm/mmu/mmu_internal.h:320 [inline]
>  kvm_mmu_page_fault+0x2f4/0x1a40 arch/x86/kvm/mmu/mmu.c:5756
>  handle_ept_violation+0x20a/0x620 arch/x86/kvm/vmx/vmx.c:5760
>  __vmx_handle_exit arch/x86/kvm/vmx/vmx.c:6539 [inline]
>  vmx_handle_exit+0x4a1/0x18d0 arch/x86/kvm/vmx/vmx.c:6556
>  vcpu_enter_guest arch/x86/kvm/x86.c:10848 [inline]
>  vcpu_run+0x24b6/0x44b0 arch/x86/kvm/x86.c:10951
>  kvm_arch_vcpu_ioctl_run+0x416/0x1830 arch/x86/kvm/x86.c:11172
>  kvm_vcpu_ioctl+0x4de/0xcc0 arch/x86/kvm/../../../virt/kvm/kvm_main.c:4112
>  vfs_ioctl fs/ioctl.c:51 [inline]
>  __do_sys_ioctl fs/ioctl.c:870 [inline]
>  __se_sys_ioctl fs/ioctl.c:856 [inline]
>  __x64_sys_ioctl+0x173/0x1e0 fs/ioctl.c:856
>  do_syscall_x64 arch/x86/entry/common.c:50 [inline]
>  do_syscall_64+0x35/0xb0 arch/x86/entry/common.c:80
>  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> RIP: 0033:0x47959d
> Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48
> 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d
> 01 f0 ff ff 73 01 c3 48 c7 c1 b4 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fc6339a4068 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
> RAX: ffffffffffffffda RBX: 000000000059c0a0 RCX: 000000000047959d
> RDX: 0000000000000000 RSI: 000000000000ae80 RDI: 0000000000000006
> RBP: 000000000059c0a0 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 000000000059c0ac
> R13: 000000000000000b R14: 0000000000437250 R15: 00007fc633984000
>  </TASK>