From: Like Xu <like.xu.linux@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>, Song Liu <songliubraving@fb.com>
Cc: bpf <bpf@vger.kernel.org>, Networking <netdev@vger.kernel.org>,
Kernel Team <Kernel-team@fb.com>,
Andrii Nakryiko <andrii@kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
like.xu@linux.intel.com
Subject: Re: bpf_get_branch_snapshot on qemu-kvm
Date: Wed, 29 Sep 2021 20:05:24 +0800 [thread overview]
Message-ID: <d75f6a9a-dbb3-c725-c001-ec9bdd55173f@gmail.com> (raw)
In-Reply-To: <YVQXT5piFYa/SEY/@hirez.programming.kicks-ass.net>
On 29/9/2021 3:35 pm, Peter Zijlstra wrote:
> On Wed, Sep 29, 2021 at 12:04:21AM +0000, Song Liu wrote:
>> Hi Peter,
>>
>> We have see the warning below while testing the new bpf_get_branch_snapshot
>> helper, on a QEMU vm (/usr/bin/qemu-system-x86_64 -enable-kvm -cpu host ...).
>> This issue doesn't happen on bare metal systems (no QEMU).
>>
>> We didn't cover this case, as LBR didn't really work in QEMU. But it seems to
>> work after I upgrade the host kernel to 5.12.
The guest LBR is enabled since the v5.12.
>>
>> At the moment, we don't have much idea on how to debug and fix the issue. Could
>> you please share your thoughts on this?
>
> Well, that's virt, afaik stuff not working is like a feature there or
> something, who knows. I've Cc'ed Like Xu who might have clue since he
> did the patches.
>
> Virt just ain't worth the pain if you ask me.
Just cc me for any vPMU/x86 stuff.
>
>>
>> Thanks in advance!
>>
>> Song
>>
>>
>>
>>
>> ============================== 8< ============================
>>
>> [ 139.494159] unchecked MSR access error: WRMSR to 0x3f1 (tried to write 0x0000000000000000) at rIP: 0xffffffff81011a8b (intel_pmu_snapshot_branch_stack+0x3b/0xd0)
Uh, it uses a PEBS counter to sample or count, which is not yet upstream but
should be soon.
Song, can you try to fix bpf_get_branch_snapshot on a normal PMC counter,
or where is the src for bpf_get_branch_snapshot? I am more than happy to help.
>> [ 139.495587] Call Trace:
>> [ 139.495845] bpf_get_branch_snapshot+0x17/0x40
>> [ 139.496285] bpf_prog_35810402cd1d294c_test1+0x33/0xe6c
>> [ 139.496791] bpf_trampoline_10737534536_0+0x4c/0x1000
>> [ 139.497274] bpf_testmod_loop_test+0x5/0x20 [bpf_testmod]
>> [ 139.497799] bpf_testmod_test_read+0x71/0x1f0 [bpf_testmod]
>> [ 139.498332] ? bpf_testmod_loop_test+0x20/0x20 [bpf_testmod]
>> [ 139.498878] ? sysfs_kf_bin_read+0xbe/0x110
>> [ 139.499284] ? bpf_testmod_loop_test+0x20/0x20 [bpf_testmod]
>> [ 139.499829] kernfs_fop_read_iter+0x1ac/0x2c0
>> [ 139.500245] ? kernfs_create_link+0x110/0x110
>> [ 139.500667] new_sync_read+0x24b/0x360
>> [ 139.501037] ? __x64_sys_llseek+0x1e0/0x1e0
>> [ 139.501444] ? rcu_read_lock_held_common+0x1a/0x50
>> [ 139.501942] ? rcu_read_lock_held_common+0x1a/0x50
>> [ 139.502404] ? rcu_read_lock_sched_held+0x5f/0xd0
>> [ 139.502865] ? rcu_read_lock_bh_held+0xb0/0xb0
>> [ 139.503294] ? security_file_permission+0xe7/0x2c0
>> [ 139.503758] vfs_read+0x1a4/0x2a0
>> [ 139.504091] ksys_read+0xc0/0x160
>> [ 139.504413] ? vfs_write+0x510/0x510
>> [ 139.504756] ? ktime_get_coarse_real_ts64+0xe4/0xf0
>> [ 139.505234] do_syscall_64+0x3a/0x80
>> [ 139.505581] entry_SYSCALL_64_after_hwframe+0x44/0xae
>> [ 139.506066] RIP: 0033:0x7fb8a05728b2
>> [ 139.506413] Code: 97 20 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b6 0f 1f 80 00 00 00 00 f3 0f 1e fa 8b 05 96 db 20 00 85 c0 75 12 31 c0 0f 05 <48> 3d 00 f0 ff ff 77 56 c3 0f 1f 44 00 00 41 54 49 89 d4 55 48 89
>> [ 139.508164] RSP: 002b:00007ffe66315a28 EFLAGS: 00000246 ORIG_RAX: 0000000000000000
>> [ 139.508870] RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fb8a05728b2
>> [ 139.509545] RDX: 0000000000000064 RSI: 0000000000000000 RDI: 0000000000000010
>> [ 139.510225] RBP: 00007ffe66315a60 R08: 0000000000000000 R09: 00007ffe66315907
>> [ 139.510897] R10: 0000000000000000 R11: 0000000000000246 R12: 000000000040c8b0
>> [ 139.511570] R13: 00007ffe66315cc0 R14: 0000000000000000 R15: 0000000000000000
next prev parent reply other threads:[~2021-09-29 12:05 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-29 0:04 Song Liu
2021-09-29 7:35 ` Peter Zijlstra
2021-09-29 12:05 ` Like Xu [this message]
2021-09-29 12:26 ` Peter Zijlstra
2021-09-29 14:42 ` Song Liu
2021-09-29 15:59 ` Peter Zijlstra
2021-09-29 16:35 ` Liang, Kan
2021-09-29 20:05 ` Song Liu
2021-10-08 3:34 ` Like Xu
2021-10-08 5:46 ` Song Liu
2021-10-08 6:36 ` Like Xu
2021-10-08 17:08 ` Song Liu
2021-10-09 9:03 ` Like Xu
2021-10-26 7:09 ` Song Liu
2021-10-28 3:09 ` Like Xu
2021-10-29 18:09 ` Song Liu
2021-09-29 23:20 ` Andi Kleen
2021-09-29 14:39 ` Song Liu
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