[tip:perf/pebs] perf, x86: Robustify PEBS fixup

tip-bot for Peter Zijlstra
2010-03-10T13:22:09Z

Commit-ID: a562b1871f7f7d2f3a835c3c1e07fa58d473cfb7
Gitweb: http://git.kernel.org/tip/a562b1871f7f7d2f3a835c3c1e07fa58d473cfb7
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Fri, 5 Mar 2010 16:29:14 +0100
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 10 Mar 2010 13:23:35 +0100

perf, x86: Robustify PEBS fixup

It turns out the LBR is massively unreliable on certain CPUs, so code the
fixup a little more defensive to avoid crashing the kernel.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Cc: paulus@samba.org
Cc: eranian@google.com
Cc: robert.richter@amd.com
Cc: fweisbec@gmail.com
LKML-Reference: <20100305154129.042271287@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
arch/x86/kernel/cpu/perf_event_intel_ds.c | 21 +++++++++++++++++++--
1 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
index a67fff1..e7ac517 100644
--- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
+++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
@@ -399,10 +399,23 @@ static int intel_pmu_pebs_fixup_ip(struct pt_regs *regs)
if (!x86_pmu.intel_cap.pebs_trap)
return 1;

+ /*
+ * No LBR entry, no basic block, no rewinding
+ */
if (!cpuc->lbr_stack.nr || !from || !to)
return 0;

- if (ip < to)
+ /*
+ * Basic blocks should never cross user/kernel boundaries
+ */
+ if (kernel_ip(ip) != kernel_ip(to))
+ return 0;
+
+ /*
+ * unsigned math, either ip is before the start (impossible) or
+ * the basic block is larger than 1 page (sanity)
+ */
+ if ((ip - to) > PAGE_SIZE)
return 0;

/*
@@ -420,7 +433,7 @@ static int intel_pmu_pebs_fixup_ip(struct pt_regs *regs)

old_to = to;
if (!kernel_ip(ip)) {
- int bytes, size = min_t(int, MAX_INSN_SIZE, ip - to);
+ int bytes, size = MAX_INSN_SIZE;

bytes = copy_from_user_nmi(buf, (void __user *)to, size);
if (bytes != size)
@@ -440,6 +453,10 @@ static int intel_pmu_pebs_fixup_ip(struct pt_regs *regs)
return 1;
}

+ /*
+ * Even though we decoded the basic block, the instruction stream
+ * never matched the given IP, either the TO or the IP got corrupted.
+ */
return 0;
}