Re: powerpc/perf: Dereference bhrb entries safely

From: Michael Ellerman
Date: Thu Dec 21 2017 - 23:43:47 EST

On Tue, 2017-12-12 at 12:29:15 UTC, Ravi Bangoria wrote:
> It may very well happen that branch instructions recorded by
> bhrb entries already get unmapped before they get processed by
> the kernel. Hence, trying to dereference such memory location
> will endup in a crash. Ex,
> Unable to handle kernel paging request for data at address 0xc008000019c41764
> Faulting instruction address: 0xc000000000084a14
> NIP [c000000000084a14] branch_target+0x4/0x70
> LR [c0000000000eb828] record_and_restart+0x568/0x5c0
> Call Trace:
> [c0000000000eb3b4] record_and_restart+0xf4/0x5c0 (unreliable)
> [c0000000000ec378] perf_event_interrupt+0x298/0x460
> [c000000000027964] performance_monitor_exception+0x54/0x70
> [c000000000009ba4] performance_monitor_common+0x114/0x120
> Fix this by deferefencing them safely.
> Suggested-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxxxxxxx>
> Reviewed-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>

Applied to powerpc fixes, thanks.