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Message-ID: <0fce42bd-1295-45a4-46b6-81b128ee343e@huawei.com>
Date: Sun, 17 Mar 2019 21:55:12 +0800
From: Zenghui Yu <yuzenghui@...wei.com>
To: Suzuki K Poulose <suzuki.poulose@....com>, <zhengxiang9@...wei.com>
CC: <marc.zyngier@....com>, <christoffer.dall@....com>,
<catalin.marinas@....com>, <will.deacon@....com>,
<james.morse@....com>, <linux-arm-kernel@...ts.infradead.org>,
<kvmarm@...ts.cs.columbia.edu>, <linux-kernel@...r.kernel.org>,
<wanghaibin.wang@...wei.com>, <lious.lilei@...ilicon.com>,
<lishuo1@...ilicon.com>
Subject: Re: [RFC] Question about TLB flush while set Stage-2 huge pages
Hi Suzuki,
On 2019/3/15 22:56, Suzuki K Poulose wrote:
> Hi Zhengui,
>
> On 15/03/2019 08:21, Zheng Xiang wrote:
>> Hi Suzuki,
>>
>> I have tested this patch, VM doesn't hang and we get expected WARNING
>> log:
>
> Thanks for the quick testing !
>
>> However, we also get the following unexpected log:
>>
>> [ 908.329900] BUG: Bad page state in process qemu-kvm pfn:a2fb41cf
>> [ 908.339415] page:ffff7e28bed073c0 count:-4 mapcount:0
>> mapping:0000000000000000 index:0x0
>> [ 908.339416] flags: 0x4ffffe0000000000()
>> [ 908.339418] raw: 4ffffe0000000000 dead000000000100 dead000000000200
>> 0000000000000000
>> [ 908.339419] raw: 0000000000000000 0000000000000000 fffffffcffffffff
>> 0000000000000000
>> [ 908.339420] page dumped because: nonzero _refcount
>> [ 908.339437] CPU: 32 PID: 72599 Comm: qemu-kvm Kdump: loaded
>> Tainted: G B W 5.0.0+ #1
>> [ 908.339438] Call trace:
>> [ 908.339439] dump_backtrace+0x0/0x188
>> [ 908.339441] show_stack+0x24/0x30
>> [ 908.339442] dump_stack+0xa8/0xcc
>> [ 908.339443] bad_page+0xf0/0x150
>> [ 908.339445] free_pages_check_bad+0x84/0xa0
>> [ 908.339446] free_pcppages_bulk+0x4b8/0x750
>> [ 908.339448] free_unref_page_commit+0x13c/0x198
>> [ 908.339449] free_unref_page+0x84/0xa0
>> [ 908.339451] __free_pages+0x58/0x68
>> [ 908.339452] zap_huge_pmd+0x290/0x2d8
>> [ 908.339454] unmap_page_range+0x2b4/0x470
>> [ 908.339455] unmap_single_vma+0x94/0xe8
>> [ 908.339457] unmap_vmas+0x8c/0x108
>> [ 908.339458] exit_mmap+0xd4/0x178
>> [ 908.339459] mmput+0x74/0x180
>> [ 908.339460] do_exit+0x2b4/0x5b0
>> [ 908.339462] do_group_exit+0x3c/0xe0
>> [ 908.339463] __arm64_sys_exit_group+0x24/0x28
>> [ 908.339465] el0_svc_common+0xa0/0x180
>> [ 908.339466] el0_svc_handler+0x38/0x78
>> [ 908.339467] el0_svc+0x8/0xc
>
> Thats bad, we seem to be making upto 4 unbalanced put_page().
>
>>>> ---
>>>> virt/kvm/arm/mmu.c | 51
>>>> +++++++++++++++++++++++++++++++++++----------------
>>>> 1 file changed, 35 insertions(+), 16 deletions(-)
>>>>
>>>> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
>>>> index 66e0fbb5..04b0f9b 100644
>>>> --- a/virt/kvm/arm/mmu.c
>>>> +++ b/virt/kvm/arm/mmu.c
>>>> @@ -1076,24 +1076,38 @@ static int stage2_set_pmd_huge(struct kvm
>>>> *kvm, struct kvm_mmu_memory_cache
>>>> * Skip updating the page table if the entry is
>>>> * unchanged.
>>>> */
>>>> - if (pmd_val(old_pmd) == pmd_val(*new_pmd))
>>>> + if (pmd_val(old_pmd) == pmd_val(*new_pmd)) {
>>>> return 0;
>>>> -
>>>> + } else if (WARN_ON_ONCE(!pmd_thp_or_huge(old_pmd))) {
>>>> /*
>>>> - * Mapping in huge pages should only happen through a
>>>> - * fault. If a page is merged into a transparent huge
>>>> - * page, the individual subpages of that huge page
>>>> - * should be unmapped through MMU notifiers before we
>>>> - * get here.
>>>> - *
>>>> - * Merging of CompoundPages is not supported; they
>>>> - * should become splitting first, unmapped, merged,
>>>> - * and mapped back in on-demand.
>>>> + * If we have PTE level mapping for this block,
>>>> + * we must unmap it to avoid inconsistent TLB
>>>> + * state. We could end up in this situation if
>>>> + * the memory slot was marked for dirty logging
>>>> + * and was reverted, leaving PTE level mappings
>>>> + * for the pages accessed during the period.
>>>> + * Normal THP split/merge follows mmu_notifier
>>>> + * callbacks and do get handled accordingly.
>>>> */
>>>> - VM_BUG_ON(pmd_pfn(old_pmd) != pmd_pfn(*new_pmd));
>>>> + unmap_stage2_range(kvm, (addr & S2_PMD_MASK),
>>>> S2_PMD_SIZE);
>>
>> It seems that kvm decreases the _refcount of the page twice in
>> transparent_hugepage_adjust()
>> and unmap_stage2_range().
>
> But I thought we should be doing that on the head_page already, as this
> is THP.
> I will take a look and get back to you on this. Btw, is it possible for you
> to turn on CONFIG_DEBUG_VM and re-run with the above patch ?
And for detailed debugging info:
I've turned on CONFIG_DEBUG_VM and re-run with your patch -- Run a guest
with stage2 PUD hugepage, enable then disable the dirty logging, and
then shutdown this guest. The result is: Host hit a kernel BUG with the
below log (when shutdown-ing guest):
[ 486.997640] kernel BUG at ./include/linux/mm.h:547!
[ 487.005524] Internal error: Oops - BUG: 0 [#1] SMP
[ 487.013455] Modules linked in: ...
[ 487.104072] CPU: 14 PID: 60747 Comm: qemu-kvm Kdump: loaded Tainted:
G W 5.0.0+ #2
[ 487.117150] ...
[ 487.135433] pstate: 40400009 (nZcv daif +PAN -UAO)
[ 487.144849] pc : unmap_stage2_puds+0x480/0x6e0
[ 487.153756] lr : unmap_stage2_puds+0x480/0x6e0
[ 487.162507] sp : ffff00002c72bb10
[ 487.179630] x27: 0000000041a00000 x26: ffff8027bbb56060
[ 487.183465] openvswitch: netlink: Tunnel attr 5 has unexpected len 1
expected 0
[ 487.189184] x25: ffff802769cbe008 x24: ffff7e0000000000
[ 487.189185] x23: ffff802769cbe008 x22: ffff00004b0af000
[ 487.189186] x21: ffff80279da06060 x20: 00400027332007fd
[ 487.189188] x19: 0000000080000000 x18: 0000000000000010
[ 487.189189] x17: 0000000000000000 x16: 0000000000000000
[ 487.189190] x15: ffff00001182d708 x14: 3030303030303030
[ 487.189191] x13: 3030303030302066 x12: ffff000011857000
[ 487.189192] x11: 0000000000000000 x10: ffff000011a48000
[ 487.189193] x9 : 0000000000000000 x8 : 0000000000000003
[ 487.189194] x7 : 000000000000095b x6 : 0000000212557560
[ 487.189196] x3 : ffff802fc0b08260 x2 : b2513adc3568f800
[ 487.189197] x1 : 0000000000000000 x0 : 000000000000003e
[ 487.189200] Process qemu-kvm (pid: 60747, stack limit =
0x000000004342b298)
[ 487.189201] Call trace:
[ 487.189203] unmap_stage2_puds+0x480/0x6e0
[ 487.189205] unmap_stage2_range+0xa4/0x190
[ 487.189208] kvm_free_stage2_pgd+0x64/0x100
[ 487.363897] kvm_arch_flush_shadow_all+0x20/0x30
[ 487.372095] kvm_mmu_notifier_release+0x3c/0x80
[ 487.380092] __mmu_notifier_release+0x50/0x100
[ 487.387914] exit_mmap+0x170/0x178
[ 487.394567] mmput+0x70/0x180
[ 487.400653] do_exit+0x2b4/0x5c8
[ 487.406849] do_group_exit+0x3c/0xe0
--[ end trace 55c414a329c80b63 ]---
[ 487.454174] Kernel panic - not syncing: Fatal exception
[ 487.461967] SMP: stopping secondary CPUs
[ 487.468473] Kernel Offset: disabled
[ 487.474520] CPU features: 0x002,22208a38
[ 487.481008] Memory Limit: none
[ 487.489095] Starting crashdump kernel...
[ 487.495457] Bye!
>
> Kind regards
> Suzuki
>
>
>
> .
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