On Wed, Sep 29, 2021 at 08:05:24PM +0800, Like Xu wrote:
> On 29/9/2021 3:35 pm, Peter Zijlstra wrote:
> > > [ 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.
Ooh that's PEBS_ENABLE
> 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.
Nah, all that code wants to do is disable PEBS... and virt being virt,
it's all sorts of weird with f/m/s :/
I so hate all that. So there's two solutions:
- get confirmation that clearing GLOBAL_CTRL is suffient to supress
PEBS, in which case we can simply remove the PEBS_ENABLE clear.
or
- create another 2 intel_pmu_snapshot_{,arch_}branch_stack() copies
that omit the PEBS thing.
