From: Peter Zijlstra <peterz@infradead.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org, Vince Weaver <vince@deater.net>,
torvalds@linux-foundation.org, robert@swiecki.net,
luto@amacapital.net, mingo@kernel.org, hughd@google.com,
greg@kroah.com,
Alexander Shishkin <alexander.shishkin@linux.intel.com>
Subject: [PATCH] x86,perf: Disable intel_bts when PTI
Date: Sun, 14 Jan 2018 11:27:13 +0100 [thread overview]
Message-ID: <20180114102713.GB6166@worktop.programming.kicks-ass.net> (raw)
The intel_bts driver does not use the 'normal' BTS buffer we allocated
space for in the cpu_entry_area but instead uses the memory allocated
for the perf AUX buffer.
This obviously comes apart when using PTI because then the kernel
mapping; which includes that AUX buffer memory; disappears.
For now disable this driver when PTI is enabled, we'll try and sort
something out later.
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Reported-by: Robert Święcki <robert@swiecki.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/x86/events/intel/bts.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/arch/x86/events/intel/bts.c b/arch/x86/events/intel/bts.c
index 141e07b06216..24ffa1e88cf9 100644
--- a/arch/x86/events/intel/bts.c
+++ b/arch/x86/events/intel/bts.c
@@ -582,6 +582,24 @@ static __init int bts_init(void)
if (!boot_cpu_has(X86_FEATURE_DTES64) || !x86_pmu.bts)
return -ENODEV;
+ if (boot_cpu_has(X86_FEATURE_PTI)) {
+ /*
+ * BTS hardware writes through a virtual memory map we must
+ * either use the kernel physical map, or the user mapping of
+ * the AUX buffer.
+ *
+ * However, since this driver supports per-CPU and per-task inherit
+ * we cannot use the user mapping since it will not be availble
+ * if we're not running the owning process.
+ *
+ * With PTI we can't use the kernal map either, because its not
+ * there when we run userspace.
+ *
+ * For now, disable this driver when using PTI.
+ */
+ return -ENODEV;
+ }
+
bts_pmu.capabilities = PERF_PMU_CAP_AUX_NO_SG | PERF_PMU_CAP_ITRACE |
PERF_PMU_CAP_EXCLUSIVE;
bts_pmu.task_ctx_nr = perf_sw_context;
next reply other threads:[~2018-01-14 10:27 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-14 10:27 Peter Zijlstra [this message]
2018-01-14 10:46 ` [tip:x86/pti] x86,perf: Disable intel_bts when PTI tip-bot for Peter Zijlstra
2018-01-14 10:50 ` [PATCH] " Greg KH
2018-01-14 10:52 ` Thomas Gleixner
2018-01-14 12:54 ` Ingo Molnar
2018-01-14 13:27 ` Greg KH
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