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Subject[tip:x86/fpu] x86/mpx: Trace the attempts to find bounds tables
Commit-ID:  2a1dcb1f796ad37028df37d96fc7c5b6b1705a43
Gitweb: http://git.kernel.org/tip/2a1dcb1f796ad37028df37d96fc7c5b6b1705a43
Author: Dave Hansen <dave.hansen@linux.intel.com>
AuthorDate: Sun, 7 Jun 2015 11:37:03 -0700
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Tue, 9 Jun 2015 12:24:32 +0200

x86/mpx: Trace the attempts to find bounds tables

There are two different events being traced here. They are
doing similar things so share a trace "EVENT_CLASS" and are
presented together.

1. Trace when MPX is zapping pages "mpx_unmap_zap":

When MPX can not free an entire bounds table, it will
instead try to zap unused parts of a bounds table to free
the backing memory. This decreases RSS (resident set
size) without decreasing the virtual space allocated
for bounds tables.

2. Trace attempts to find bounds tables "mpx_unmap_search":

This event traces any time we go looking to unmap a
bounds table for a given virtual address range. This is
useful to ensure that the kernel actually "tried" to free
a bounds table versus times it succeeded in finding one.

It might try and fail if it realized that a table was
shared with an adjacent VMA which is not being unmapped.

Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Dave Hansen <dave@sr71.net>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20150607183703.B9D2468B@viggo.jf.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/include/asm/trace/mpx.h | 32 ++++++++++++++++++++++++++++++++
arch/x86/mm/mpx.c | 2 ++
2 files changed, 34 insertions(+)

diff --git a/arch/x86/include/asm/trace/mpx.h b/arch/x86/include/asm/trace/mpx.h
index 5c3af06..c13c6fa 100644
--- a/arch/x86/include/asm/trace/mpx.h
+++ b/arch/x86/include/asm/trace/mpx.h
@@ -63,6 +63,38 @@ TRACE_EVENT(bounds_exception_mpx,
__entry->bndstatus)
);

+DECLARE_EVENT_CLASS(mpx_range_trace,
+
+ TP_PROTO(unsigned long start,
+ unsigned long end),
+ TP_ARGS(start, end),
+
+ TP_STRUCT__entry(
+ __field(unsigned long, start)
+ __field(unsigned long, end)
+ ),
+
+ TP_fast_assign(
+ __entry->start = start;
+ __entry->end = end;
+ ),
+
+ TP_printk("[0x%p:0x%p]",
+ (void *)__entry->start,
+ (void *)__entry->end
+ )
+);
+
+DEFINE_EVENT(mpx_range_trace, mpx_unmap_zap,
+ TP_PROTO(unsigned long start, unsigned long end),
+ TP_ARGS(start, end)
+);
+
+DEFINE_EVENT(mpx_range_trace, mpx_unmap_search,
+ TP_PROTO(unsigned long start, unsigned long end),
+ TP_ARGS(start, end)
+);
+
#else

/*
diff --git a/arch/x86/mm/mpx.c b/arch/x86/mm/mpx.c
index 75e5d70..55729ee 100644
--- a/arch/x86/mm/mpx.c
+++ b/arch/x86/mm/mpx.c
@@ -668,6 +668,7 @@ static int zap_bt_entries(struct mm_struct *mm,

len = min(vma->vm_end, end) - addr;
zap_page_range(vma, addr, len, NULL);
+ trace_mpx_unmap_zap(addr, addr+len);

vma = vma->vm_next;
addr = vma->vm_start;
@@ -840,6 +841,7 @@ static int mpx_unmap_tables(struct mm_struct *mm,
long __user *bd_entry, *bde_start, *bde_end;
unsigned long bt_addr;

+ trace_mpx_unmap_search(start, end);
/*
* "Edge" bounds tables are those which are being used by the region
* (start -> end), but that may be shared with adjacent areas. If they

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