Commit 99a9dc98 authored Jan 14, 2018 by Peter Zijlstra Committed by Thomas Gleixner Jan 14, 2018

x86,perf: Disable intel_bts when PTI



The intel_bts driver does not use the 'normal' BTS buffer which is exposed
through 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. Fixing this requires to
expose a mapping which is visible in all context and that's not trivial.

As a quick fix disable this driver when PTI is enabled to prevent
malfunction.

Fixes: 385ce0ea ("x86/mm/pti: Add Kconfig")
Reported-by: Vince Weaver <vincent.weaver@maine.edu>
Reported-by: Robert Święcki <robert@swiecki.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: greg@kroah.com
Cc: hughd@google.com
Cc: luto@amacapital.net
Cc: Vince Weaver <vince@deater.net>
Cc: torvalds@linux-foundation.org
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20180114102713.GB6166@worktop.programming.kicks-ass.net

parent a237f762

arch/x86/events/intel/bts.c

+18 −0

Original line number	Diff line number	Diff line
		@@ -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;

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