Message-ID: <4FD649CF.5020300@fb.com>
Date: Mon, 11 Jun 2012 12:41:03 -0700
From: Arun Sharma <asharma@fb.com>
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To: Peter Zijlstra <peterz@infradead.org>
CC: Stephane Eranian <eranian@google.com>, <linux-kernel@vger.kernel.org>,
        <mingo@elte.hu>
Subject: Re: [PATCH] perf/x86: fix broken LBR fixup code
References: <20120611134426.GA7542@quad> <1339422464.30462.17.camel@twins>
In-Reply-To: <1339422464.30462.17.camel@twins>
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On 6/11/12 6:47 AM, Peter Zijlstra wrote:
> On Mon, 2012-06-11 at 15:44 +0200, Stephane Eranian wrote:
>> I noticed that the LBR fixups were not working anymore
>> on programs where they used to. I tracked this down to
>> a recent change to copy_from_user_nmi().
>>
>> commit db0dc75d6403b6663c0eab4c6ccb672eb9b2ed72
>> Author: Arun Sharma<asharma@fb.com>
>> Date:   Fri Apr 20 15:41:36 2012 -0700
>>
>>      perf/x86: Check user address explicitly in copy_from_user_nmi()
>>
>> This commit added a call to __range_not_ok() to the
>> copy_from_user_nmi() routine. The problem is that the logic
>> of the test must be reversed. __range_not_ok() returns 0 if the
>> range is VALID. We want to return early from copy_from_user_nmi()
>> if the range is NOT valid.
>
> D'0h.. Thanks!

My bad. I was fooled by all the kernel addresses that were unwound 
properly. Didn't notice the broken unwinding in user space before I sent 
the patch. The fix looks good. Thanks.

  -Arun
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