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Message-ID: <75f6aba1-8ed6-4ef8-8811-de40ae40be90@amd.com>
Date: Thu, 30 May 2024 09:07:30 +0530
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH] perf/x86/amd: check event before enable to avoid GPF
To: George Kennedy <george.kennedy@oracle.com>
Cc: harshit.m.mogalapalli@oracle.com, peterz@infradead.org, mingo@redhat.com,
 acme@kernel.org, namhyung@kernel.org, mark.rutland@arm.com,
 alexander.shishkin@linux.intel.com, jolsa@kernel.org, irogers@google.com,
 adrian.hunter@intel.com, kan.liang@linux.intel.com, tglx@linutronix.de,
 bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com,
 linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
 ravi.bangoria@amd.com
References: <1716990659-2427-1-git-send-email-george.kennedy@oracle.com>
Content-Language: en-US
From: Ravi Bangoria <ravi.bangoria@amd.com>
In-Reply-To: <1716990659-2427-1-git-send-email-george.kennedy@oracle.com>
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Hi George,

> Events can be deleted and the entry can be NULL.

Can you please also explain "how".

> Check event for NULL in amd_pmu_enable_all() before enable to avoid a GPF.
> This appears to be an AMD only issue.
> 
> Syzkaller reported a GPF in amd_pmu_enable_all.

Can you please provide a bug report link? Also, any reproducer?

> @@ -760,7 +760,8 @@ static void amd_pmu_enable_all(int added)
>  		if (!test_bit(idx, cpuc->active_mask))
>  			continue;
>  
> -		amd_pmu_enable_event(cpuc->events[idx]);
> +		if (cpuc->events[idx])
> +			amd_pmu_enable_event(cpuc->events[idx]);

What if cpuc->events[idx] becomes NULL after if (cpuc->events[idx]) but
before amd_pmu_enable_event(cpuc->events[idx])?

Thanks,
Ravi