On Wed, Apr 01, 2020 at 08:50:55PM +0800, Zhuang Yanying wrote:
> We are testing Virtual Machine with KSM on v5.4-rc2 kernel,
> and found the zero_page refcount overflow.
> The cause of refcount overflow is increased in try_async_pf
> (get_user_page) without being decreased in mmu_set_spte()
> while handling ept violation.
> In kvm_release_pfn_clean(), only unreserved page will call
> put_page. However, zero page is reserved.
> So, as well as creating and destroy vm, the refcount of
> zero page will continue to increase until it overflows.
>
> step1:
> echo 10000 > /sys/kernel/mm/ksm/pages_to_scan
> echo 1 > /sys/kernel/mm/ksm/run
> echo 1 > /sys/kernel/mm/ksm/use_zero_pages
>
> step2:
> just create several normal qemu kvm vms.
> And destroy it after 10s.
> Repeat this action all the time.
>
> After a long period of time, all domains hang because
> of the refcount of zero page overflow.
>
> Qemu print error log as follow:
> error: kvm run failed Bad address
> EAX=00006cdc EBX=00000008 ECX=80202001 EDX=078bfbfd
> ESI=ffffffff EDI=00000000 EBP=00000008 ESP=00006cc4
> EIP=000efd75 EFL=00010002 [-------] CPL=0 II=0 A20=1 SMM=0 HLT=0
> ES =0010 00000000 ffffffff 00c09300 DPL=0 DS [-WA]
> CS =0008 00000000 ffffffff 00c09b00 DPL=0 CS32 [-RA]
> SS =0010 00000000 ffffffff 00c09300 DPL=0 DS [-WA]
> DS =0010 00000000 ffffffff 00c09300 DPL=0 DS [-WA]
> FS =0010 00000000 ffffffff 00c09300 DPL=0 DS [-WA]
> GS =0010 00000000 ffffffff 00c09300 DPL=0 DS [-WA]
> LDT=0000 00000000 0000ffff 00008200 DPL=0 LDT
> TR =0000 00000000 0000ffff 00008b00 DPL=0 TSS32-busy
> GDT= 000f7070 00000037
> IDT= 000f70ae 00000000
> CR0=00000011 CR2=00000000 CR3=00000000 CR4=00000000
> DR0=0000000000000000 DR1=0000000000000000 DR2=0000000000000000 DR3=0000000000000000
> DR6=00000000ffff0ff0 DR7=0000000000000400
> EFER=0000000000000000
> Code=00 01 00 00 00 e9 e8 00 00 00 c7 05 4c 55 0f 00 01 00 00 00 <8b> 35 00 00 01 00 8b 3d 04 00 01 00 b8 d8 d3 00 00 c1 e0 08 0c ea a3 00 00 01 00 c7 05 04
>
> Meanwhile, a kernel warning is departed.
>
> [40914.836375] WARNING: CPU: 3 PID: 82067 at ./include/linux/mm.h:987 try_get_page+0x1f/0x30
> [40914.836412] CPU: 3 PID: 82067 Comm: CPU 0/KVM Kdump: loaded Tainted: G OE 5.2.0-rc2 #5
> [40914.836415] RIP: 0010:try_get_page+0x1f/0x30
> [40914.836417] Code: 40 00 c3 0f 1f 84 00 00 00 00 00 48 8b 47 08 a8 01 75 11 8b 47 34 85 c0 7e 10 f0 ff 47 34 b8 01 00 00 00 c3 48 8d 78 ff eb e9 <0f> 0b 31 c0 c3 66 90 66 2e 0f 1f 84 00 0
> 0 00 00 00 48 8b 47 08 a8
> [40914.836418] RSP: 0018:ffffb4144e523988 EFLAGS: 00010286
> [40914.836419] RAX: 0000000080000000 RBX: 0000000000000326 RCX: 0000000000000000
> [40914.836420] RDX: 0000000000000000 RSI: 00004ffdeba10000 RDI: ffffdf07093f6440
> [40914.836421] RBP: ffffdf07093f6440 R08: 800000424fd91225 R09: 0000000000000000
> [40914.836421] R10: ffff9eb41bfeebb8 R11: 0000000000000000 R12: ffffdf06bbd1e8a8
> [40914.836422] R13: 0000000000000080 R14: 800000424fd91225 R15: ffffdf07093f6440
> [40914.836423] FS: 00007fb60ffff700(0000) GS:ffff9eb4802c0000(0000) knlGS:0000000000000000
> [40914.836425] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> [40914.836426] CR2: 0000000000000000 CR3: 0000002f220e6002 CR4: 00000000003626e0
> [40914.836427] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [40914.836427] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> [40914.836428] Call Trace:
> [40914.836433] follow_page_pte+0x302/0x47b
> [40914.836437] __get_user_pages+0xf1/0x7d0
> [40914.836441] ? irq_work_queue+0x9/0x70
> [40914.836443] get_user_pages_unlocked+0x13f/0x1e0
> [40914.836469] __gfn_to_pfn_memslot+0x10e/0x400 [kvm]
> [40914.836486] try_async_pf+0x87/0x240 [kvm]
> [40914.836503] tdp_page_fault+0x139/0x270 [kvm]
> [40914.836523] kvm_mmu_page_fault+0x76/0x5e0 [kvm]
> [40914.836588] vcpu_enter_guest+0xb45/0x1570 [kvm]
> [40914.836632] kvm_arch_vcpu_ioctl_run+0x35d/0x580 [kvm]
> [40914.836645] kvm_vcpu_ioctl+0x26e/0x5d0 [kvm]
> [40914.836650] do_vfs_ioctl+0xa9/0x620
> [40914.836653] ksys_ioctl+0x60/0x90
> [40914.836654] __x64_sys_ioctl+0x16/0x20
> [40914.836658] do_syscall_64+0x5b/0x180
> [40914.836664] entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [40914.836666] RIP: 0033:0x7fb61cb6bfc7
>
> Signed-off-by: LinFeng <linfeng23@xxxxxxxxxx>
> Signed-off-by: Zhuang Yanying <ann.zhuangyanying@xxxxxxxxxx>
> ---
> virt/kvm/kvm_main.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 7e80f62f034c..7f7c22a687c0 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -133,7 +133,8 @@ static bool largepages_enabled = true;
> bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
> {
> if (pfn_valid(pfn))
> - return PageReserved(pfn_to_page(pfn));
> + return PageReserved(pfn_to_page(pfn)) &&
> + !is_zero_pfn(pfn);
>
> return true;
> }
> --
> 2.23.0
>
>
<formletter>
This is not the correct way to submit patches for inclusion in the
stable kernel tree. Please read:
https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html
for how to do this properly.
</formletter>
