From: Leo Yan <leo.yan@linaro.org>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Mathieu Poirier <mathieu.poirier@linaro.org>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
Mike Leach <mike.leach@linaro.org>,
Andi Kleen <ak@linux.intel.com>,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
coresight@lists.linaro.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 8/8] perf record: Directly bail out for compat case
Date: Wed, 9 Jun 2021 16:57:41 +0800 [thread overview]
Message-ID: <20210609085741.GF4640@leoy-ThinkPad-X240s> (raw)
In-Reply-To: <d87d8fd8-c6f1-9d9b-5c2e-629588123a9c@intel.com>
Hi Adrian,
On Wed, Jun 09, 2021 at 11:23:25AM +0300, Adrian Hunter wrote:
[...]
> >> I was thinking we would separate out the compat case:
> >>
> >> #if BITS_PER_LONG == 32
> >> if (kernel_is_64_bit)
> >> return compat_auxtrace_mmap__[read_head/write_tail]()
> >> #endif
> >>
> >> So the non-compat cases would not be affected.
> >
> > Because I don't want to introduce the complexity for read/write head
> > and tail, and we also need to handle the same issue for the perf ring
> > buffer. So how about below change?
> >
> > The main idea for below change is it allows the perf to run normally
> > on the compat mode and exitly if detects the buffer head is close to
> > the low 32-bit's overflow: when detect the low 32-bit value is bigger
> > than 0xf0000000 (so we have 256MiB margin to the overflow), it reports
> > error and exit.
> >
> > diff --git a/tools/perf/util/auxtrace.c b/tools/perf/util/auxtrace.c
> > index 1b4091a3b508..2a9965bfeab4 100644
> > --- a/tools/perf/util/auxtrace.c
> > +++ b/tools/perf/util/auxtrace.c
> > @@ -1693,6 +1693,14 @@ static int __auxtrace_mmap__read(struct mmap *map,
> > pr_debug3("auxtrace idx %d old %#"PRIx64" head %#"PRIx64" diff %#"PRIx64"\n",
> > mm->idx, old, head, head - old);
> >
> > +#ifdef BITS_PER_LONG == 32
> > + if (kernel_is_64bit() && head >= 0xf0000000) {
>
> You are assuming the head never increases by more than 256MiB which
> means you should limit the buffer size to 256MiB maximum.
>
> To me this seems a bit too far from an ideal solution.
>
> I would have thought separating out the compat case makes things
> simpler to understand.
Agreed. I will follow up the suggestions to add compat variants for
accessing AUX head and tail, and will distinguish compat case with
global env variable for 64-bit kernel.
After get ready, will send out for review. Thanks a lot for suggestions!
Leo
prev parent reply other threads:[~2021-06-09 8:58 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-02 10:29 [PATCH v2 0/8] perf: Refine barriers for AUX ring buffer Leo Yan
2021-06-02 10:30 ` [PATCH v2 1/8] perf/ring_buffer: Add comment for barriers on " Leo Yan
2021-06-07 15:27 ` Peter Zijlstra
2021-06-02 10:30 ` [PATCH v2 2/8] coresight: tmc-etr: Add barrier after updating " Leo Yan
2021-06-02 10:30 ` [PATCH v2 3/8] coresight: tmc-etf: Add comment for store ordering Leo Yan
2021-06-02 10:30 ` [PATCH v2 4/8] perf/x86: Add barrier after updating bts Leo Yan
2021-06-07 15:29 ` Peter Zijlstra
2021-06-02 10:30 ` [PATCH v2 5/8] perf auxtrace: Change to use SMP memory barriers Leo Yan
2021-06-07 10:02 ` Adrian Hunter
2021-06-07 15:29 ` Peter Zijlstra
2021-06-08 16:45 ` Arnaldo Carvalho de Melo
2021-06-02 10:30 ` [PATCH v2 6/8] perf auxtrace: Drop legacy __sync functions Leo Yan
2021-06-02 10:47 ` Adrian Hunter
2021-06-02 11:16 ` Leo Yan
2021-06-02 11:21 ` Adrian Hunter
2021-06-02 13:01 ` Leo Yan
2021-06-02 10:30 ` [PATCH v2 7/8] perf auxtrace: Use WRITE_ONCE() for updating aux_tail Leo Yan
2021-06-07 10:03 ` Adrian Hunter
2021-06-07 15:31 ` Peter Zijlstra
2021-06-08 17:04 ` Arnaldo Carvalho de Melo
2021-06-09 0:21 ` Leo Yan
2021-06-02 10:30 ` [PATCH v2 8/8] perf record: Directly bail out for compat case Leo Yan
2021-06-02 11:18 ` Adrian Hunter
2021-06-02 12:38 ` Leo Yan
2021-06-07 10:23 ` Adrian Hunter
2021-06-07 15:09 ` Leo Yan
2021-06-09 8:23 ` Adrian Hunter
2021-06-09 8:57 ` Leo Yan [this message]
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