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>
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 @@
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 @@
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 @@
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;
}