Re: [PATCH] kvm: x86: move tracepoints outside extended quiescent state

[Borislav Petkov <bp@alien8.de>]

On Fri, Dec 11, 2015 at 11:41:30AM +0100, Paolo Bonzini wrote:
> You can disable it (well, make it take a few days to appear) with this:
> 
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 484079efea5b..a9070e260c72 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -496,7 +496,7 @@ static struct kvm_memslots *kvm_alloc_memslots(void)
>  	 * Init kvm generation close to the maximum to easily test the
>  	 * code of handling generation number wrap-around.
>  	 */
> -	slots->generation = -150;
> +	slots->generation = 0;
>  	for (i = 0; i < KVM_MEM_SLOTS_NUM; i++)
>  		slots->id_to_index[i] = slots->memslots[i].id = i;
> 
> but it would not be AMD-specific.

Yeah, that didn't help. This time the splat is a bit more interesting:

qemu process segfaulted at a kernel address - ffffffff816e2db1 - which
is the last insn of entry_SYSCALL_64_fastpath:

ffffffff816e2d45 <entry_SYSCALL_64_fastpath>:
ffffffff816e2d45:       25 ff ff ff bf          and    $0xbfffffff,%eax
ffffffff816e2d4a:       3d 21 02 00 00          cmp    $0x221,%eax

...

ffffffff816e2d9e:       4c 8b 9c 24 90 00 00    mov    0x90(%rsp),%r11
ffffffff816e2da5:       00 
ffffffff816e2da6:       48 8b a4 24 98 00 00    mov    0x98(%rsp),%rsp
ffffffff816e2dad:       00 
ffffffff816e2dae:       0f 01 f8                swapgs
ffffffff816e2db1:       48 0f 07                sysretq

Yap, at SYSRET.

Andy might find this a little amusing :-)

[  459.130565] qemu-system-x86[3724]: segfault at ffffffff816e2db1 ip ffffffff816e2db1 sp 00007fd593ffe970 error 15
[  512.578297] BUG: unable to handle kernel NULL pointer dereference at           (null)
[  512.586189] IP: [<          (null)>]           (null)
[  512.591266] PGD 0 
[  512.593303] Oops: 0010 [#1] PREEMPT SMP 
[  512.597283] Modules linked in: tun sha256_ssse3 sha256_generic drbg binfmt_misc ipv6 vfat fat fuse dm_crypt dm_mod kvm_amd kvm irqbypass crc32_pclmul aesni_intel aes_x86_64 lrw gf128mul glue_helper ablk_helper cryptd amd64_edac_mod k10temp edac_mce_amd fam15h_power amdkfd amd_iommu_v2 radeon acpi_cpufreq
[  512.601698] CPU: 5 PID: 3787 Comm: qemu-system-x86 Not tainted 4.4.0-rc4+ #8
[  512.601699] Hardware name: To be filled by O.E.M. To be filled by O.E.M./M5A97 EVO R2.0, BIOS 1503 01/16/2013
[  512.601700] task: ffff8800b5d04680 ti: ffff88041104c000 task.ti: ffff88041104c000
[  512.601701] RIP: 0010:[<0000000000000000>] 
[  512.601701]  [<          (null)>]           (null)
[  512.601702] RSP: 0018:ffff88041104fcc0  EFLAGS: 00010212
[  512.601703] RAX: 0000000000000040 RBX: ffff8804110b4000 RCX: 0000000000000000
[  512.601703] RDX: 0000000000000000 RSI: ffff8804110b4000 RDI: ffff88041104fc20
[  512.601704] RBP: ffff88041104fcc8 R08: 0000000000000001 R09: 0000000000000000
[  512.601704] R10: 0000000000000001 R11: 0000000000000001 R12: 00000000ffffffff
[  512.601705] R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000001
[  512.601706] FS:  00007fb0deaf4700(0000) GS:ffff88042d000000(0000) knlGS:0000000000000000
[  512.601706] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
[  512.601707] CR2: 0000000000000000 CR3: 0000000428118000 CR4: 00000000000406e0
[  512.601707] Stack:
[  512.601708]  ffffffffa02b2d3c
[  512.601708]  ffff88041104fdd8
[  512.601709]  ffffffffa02b2d0e
[  512.601709]  ffffffffa02b2c9a

[  512.601710]  ffff8804110b4430
[  512.601710]  0000000000000000
[  512.601710]  0000000100000004
[  512.601711]  ffffffffa02e9bb0

[  512.601711]  0000000400000002
[  512.601711]  0000000000000000
[  512.601712]  0000000000000000
[  512.601712]  0000000000000000

[  512.601713] Call Trace:
[  512.601729]  [<ffffffffa02b2d3c>] ? kvm_set_irq+0x13c/0x250 [kvm]
[  512.601736]  [<ffffffffa02b2d0e>] kvm_set_irq+0x10e/0x250 [kvm]
[  512.601744]  [<ffffffffa02b2c9a>] ? kvm_set_irq+0x9a/0x250 [kvm]
[  512.601756]  [<ffffffffa02e9bb0>] ? kvm_set_msi_irq+0x1b0/0x1b0 [kvm]
[  512.601767]  [<ffffffffa02e9bd0>] ? kvm_set_ioapic_irq+0x20/0x20 [kvm]
[  512.601776]  [<ffffffffa02c2612>] kvm_vm_ioctl_irq_line+0x32/0x40 [kvm]
[  512.601783]  [<ffffffffa02af97b>] kvm_vm_ioctl+0x5eb/0x820 [kvm]
[  512.601786]  [<ffffffff810c6a25>] ? rcu_read_lock_held+0x45/0x60
[  512.601788]  [<ffffffff811a0930>] do_vfs_ioctl+0x2e0/0x540
[  512.601790]  [<ffffffff811ac8e9>] ? __fget_light+0x29/0x90
[  512.601791]  [<ffffffff811a0bdc>] SyS_ioctl+0x4c/0x90
[  512.601794]  [<ffffffff816e2d5b>] entry_SYSCALL_64_fastpath+0x16/0x6f
[  512.601797] Code:  Bad RIP value.
[  512.601798] RIP  [<          (null)>]           (null)
[  512.601798]  RSP <ffff88041104fcc0>
[  512.601799] CR2: 0000000000000000
[  512.609862] ---[ end trace ae4f00b514141891 ]---

-- 
Regards/Gruss,
    Boris.

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