lkml.org 
[lkml]   [2022]   [Nov]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [Syzkaller & bisect] There is "__perf_event_overflow" WARNING in v6.1-rc5 kernel in guest
Hi Peter,

On 2022-11-23 at 16:05:14 +0100, Peter Zijlstra wrote:
> On Sat, Nov 19, 2022 at 10:45:54AM +0800, Pengfei Xu wrote:
>
> > The result shows that your additional patch fixed this issue!
> > If possible, could you add Reported-and-tested-by tag from me.
>
> After talking with Marco for a bit the patch now looks like the below.
> I've tentatively retained your tested-by, except of course, you haven't.
>
> If I could bother you once more to test the branch:
>
> git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git perf/urgent
>
Yes, sure, it's my pleasure! I will clone and test the origin/perf/urgent
branch in this repo and update the email soon.
git clone git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git time
out in my side, and I git cloned https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git,
it should be the same repo.

Thanks!
BR.

> ---
> Subject: perf: Consider OS filter fail
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Sat, 19 Nov 2022 10:45:54 +0800
>
> Some PMUs (notably the traditional hardware kind) have boundary issues
> with the OS filter. Specifically, it is possible for
> perf_event_attr::exclude_kernel=1 events to trigger in-kernel due to
> SKID or errata.
>
> This can upset the sigtrap logic some and trigger the WARN.
>
> However, if this invalid sample is the first we must not loose the
> SIGTRAP, OTOH if it is the second, it must not override the
> pending_addr with an invalid one.
>
> Fixes: ca6c21327c6a ("perf: Fix missing SIGTRAPs")
> Reported-by: Pengfei Xu <pengfei.xu@intel.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Tested-by: Pengfei Xu <pengfei.xu@intel.com>
> Link: https://lkml.kernel.org/r/Y3hDYiXwRnJr8RYG@xpf.sh.intel.com
> ---
> kernel/events/core.c | 24 ++++++++++++++++++++++--
> 1 file changed, 22 insertions(+), 2 deletions(-)
>
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9273,6 +9273,19 @@ int perf_event_account_interrupt(struct
> return __perf_event_account_interrupt(event, 1);
> }
>
> +static inline bool sample_is_allowed(struct perf_event *event, struct pt_regs *regs)
> +{
> + /*
> + * Due to interrupt latency (AKA "skid"), we may enter the
> + * kernel before taking an overflow, even if the PMU is only
> + * counting user events.
> + */
> + if (event->attr.exclude_kernel && !user_mode(regs))
> + return false;
> +
> + return true;
> +}
> +
> /*
> * Generic event overflow handling, sampling.
> */
> @@ -9306,6 +9319,13 @@ static int __perf_event_overflow(struct
> }
>
> if (event->attr.sigtrap) {
> + /*
> + * The desired behaviour of sigtrap vs invalid samples is a bit
> + * tricky; on the one hand, one should not loose the SIGTRAP if
> + * it is the first event, on the other hand, we should also not
> + * trigger the WARN or override the data address.
> + */
> + bool valid_sample = sample_is_allowed(event, regs);
> unsigned int pending_id = 1;
>
> if (regs)
> @@ -9313,7 +9333,7 @@ static int __perf_event_overflow(struct
> if (!event->pending_sigtrap) {
> event->pending_sigtrap = pending_id;
> local_inc(&event->ctx->nr_pending);
> - } else if (event->attr.exclude_kernel) {
> + } else if (event->attr.exclude_kernel && valid_sample) {
> /*
> * Should not be able to return to user space without
> * consuming pending_sigtrap; with exceptions:
> @@ -9330,7 +9350,7 @@ static int __perf_event_overflow(struct
> }
>
> event->pending_addr = 0;
> - if (data->sample_flags & PERF_SAMPLE_ADDR)
> + if (valid_sample && (data->sample_flags & PERF_SAMPLE_ADDR))
> event->pending_addr = data->addr;
> irq_work_queue(&event->pending_irq);
> }

\
 
 \ /
  Last update: 2022-11-23 16:28    [W:0.233 / U:0.104 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site