From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B99F81D5AA0; Sun, 24 Nov 2024 12:41:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732452091; cv=none; b=pOGa0LsLi2a1l+n3XHNHVIUV7s4svh7EP06pZ4k1OYC9u/tsv447Nz6tq8El3Ma1C0xmpGX2KmbtsPebJMdVaOf1pH6RJKU/HgQUnXXC8fAqa3D5z/fo6pOzTXOD2FCRq+m+dpA3bSNk7dpELE2b3D6dwSKxlX6FB2sg5FXpXHA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732452091; c=relaxed/simple; bh=UUHYHnBG5cAPyJVlWiM8ygRmpTF7s2XShHfc1Btr4eM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=T43xku4Uwumjfm8CDCZ6VwZinBx+jzmxgbNA2XTkSzsFEd2j0ECXVWNMHYnjliPFTb0gndA7hS4tYuXzcMz3l+eknvR1jBJpY2gRpvQeg4FXnUilB6xlNnBbX4nMmt0fwpD514epM9Np2BfVsNPJd1nE3RQFh7Hd8qYYN0CoLak= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=B5Wbx7cL; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="B5Wbx7cL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 890A1C4CECC; Sun, 24 Nov 2024 12:41:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1732452091; bh=UUHYHnBG5cAPyJVlWiM8ygRmpTF7s2XShHfc1Btr4eM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=B5Wbx7cLxG99b6TnXZ1JGVjF5Xzr+USd4cg+P9U9kLNNAmGaybB3RdLDQ4TnQnpVA 9UXN7W7tQpLBfY+9mIS+D5uG7SimhDC8XDTp4DzG1j1xli2080lpCmMErJuGJPfMGF vCaSAjJM0o7t50utZEut+qj/BUtSPmExLl1kD4xK6IHs1rLiIBn/PyhHj948D+jloN j9KDUaS3ckHiuE4/zlPLBe1Um7mngYpl3ACRcAeGFW/mFZbJFy1I3kFX9VNAJgHDI6 Sr2J2PR4tT5ePmQN7SKoPnBd882083OfoavVbxOmRNx082ZmX6GoJPbdoR9OIqE3fv wKpqtbdXRiOkA== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Thomas Richter , Hendrik Brueckner , Heiko Carstens , Sasha Levin , gor@linux.ibm.com, agordeev@linux.ibm.com, sumanthk@linux.ibm.com, linux-s390@vger.kernel.org Subject: [PATCH AUTOSEL 6.1 2/7] s390/cpum_sf: Handle CPU hotplug remove during sampling Date: Sun, 24 Nov 2024 07:41:13 -0500 Message-ID: <20241124124126.3336691-2-sashal@kernel.org> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20241124124126.3336691-1-sashal@kernel.org> References: <20241124124126.3336691-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore X-stable-base: Linux 6.1.119 Content-Transfer-Encoding: 8bit From: Thomas Richter [ Upstream commit a0bd7dacbd51c632b8e2c0500b479af564afadf3 ] CPU hotplug remove handling triggers the following function call sequence: CPUHP_AP_PERF_S390_SF_ONLINE --> s390_pmu_sf_offline_cpu() ... CPUHP_AP_PERF_ONLINE --> perf_event_exit_cpu() The s390 CPUMF sampling CPU hotplug handler invokes: s390_pmu_sf_offline_cpu() +--> cpusf_pmu_setup() +--> setup_pmc_cpu() +--> deallocate_buffers() This function de-allocates all sampling data buffers (SDBs) allocated for that CPU at event initialization. It also clears the PMU_F_RESERVED bit. The CPU is gone and can not be sampled. With the event still being active on the removed CPU, the CPU event hotplug support in kernel performance subsystem triggers the following function calls on the removed CPU: perf_event_exit_cpu() +--> perf_event_exit_cpu_context() +--> __perf_event_exit_context() +--> __perf_remove_from_context() +--> event_sched_out() +--> cpumsf_pmu_del() +--> cpumsf_pmu_stop() +--> hw_perf_event_update() to stop and remove the event. During removal of the event, the sampling device driver tries to read out the remaining samples from the sample data buffers (SDBs). But they have already been freed (and may have been re-assigned). This may lead to a use after free situation in which case the samples are most likely invalid. In the best case the memory has not been reassigned and still contains valid data. Remedy this situation and check if the CPU is still in reserved state (bit PMU_F_RESERVED set). In this case the SDBs have not been released an contain valid data. This is always the case when the event is removed (and no CPU hotplug off occured). If the PMU_F_RESERVED bit is not set, the SDB buffers are gone. Signed-off-by: Thomas Richter Reviewed-by: Hendrik Brueckner Signed-off-by: Heiko Carstens Signed-off-by: Sasha Levin --- arch/s390/kernel/perf_cpum_sf.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/s390/kernel/perf_cpum_sf.c b/arch/s390/kernel/perf_cpum_sf.c index f3b0a106f7227..46a1a85a0e440 100644 --- a/arch/s390/kernel/perf_cpum_sf.c +++ b/arch/s390/kernel/perf_cpum_sf.c @@ -1896,7 +1896,9 @@ static void cpumsf_pmu_stop(struct perf_event *event, int flags) event->hw.state |= PERF_HES_STOPPED; if ((flags & PERF_EF_UPDATE) && !(event->hw.state & PERF_HES_UPTODATE)) { - hw_perf_event_update(event, 1); + /* CPU hotplug off removes SDBs. No samples to extract. */ + if (cpuhw->flags & PMU_F_RESERVED) + hw_perf_event_update(event, 1); event->hw.state |= PERF_HES_UPTODATE; } perf_pmu_enable(event->pmu); -- 2.43.0