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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