From: Peter Zijlstra <peterz@infradead.org>
To: Andi Kleen <andi@firstfloor.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH 2/2] x86, perf: Optimize stack walk user accesses
Date: Tue, 20 Oct 2015 13:03:32 +0200 [thread overview]
Message-ID: <20151020110332.GB17308@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <1445295269-5672-2-git-send-email-andi@firstfloor.org>
On Mon, Oct 19, 2015 at 03:54:29PM -0700, Andi Kleen wrote:
> @@ -2307,7 +2312,13 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
> frame.next_frame = NULL;
> frame.return_address = 0;
>
> - bytes = copy_from_user_nmi(&frame, fp, sizeof(frame));
> + if (!access_ok(VERIFY_READ, fp, 16))
> + break;
> +
> + bytes = __copy_from_user_nmi(&frame.next_frame, fp, 8);
> + if (bytes != 0)
> + break;
> + bytes = __copy_from_user_nmi(&frame.return_address, fp+8, 8);
> if (bytes != 0)
> break;
>
The previous patch that introduces this function states that any caller
must have pagefault_disable() or be from interrupt context.
Perf can call this function from !interrupt context (imagine a
tracepoint or other software event), should we therefore not add a
pagefault_disable()/enable() pair around the entire while() loop?
next prev parent reply other threads:[~2015-10-20 11:03 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-10-19 22:54 [PATCH 1/2] x86: Add a __copy_from_user_nmi Andi Kleen
2015-10-19 22:54 ` [PATCH 2/2] x86, perf: Optimize stack walk user accesses Andi Kleen
2015-10-20 11:03 ` Peter Zijlstra [this message]
2015-10-20 17:32 ` Andi Kleen
2015-10-22 22:07 [PATCH 1/2] x86: Add a __copy_from_user_nmi Andi Kleen
2015-10-22 22:07 ` [PATCH 2/2] x86, perf: Optimize stack walk user accesses Andi Kleen
2015-11-16 23:23 [PATCH 1/2] x86: Add a __copy_from_user_nmi Andi Kleen
2015-11-16 23:23 ` [PATCH 2/2] x86, perf: Optimize stack walk user accesses Andi Kleen
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