When an interrupt (such as a perf counter interrupt) is delivered
while executing in user space, the trap entry code puts ASI_AIUS in
%asi so that copy_from_user() and copy_to_user() will access the
correct memory. But if a perf counter interrupt is delivered while the
cpu is already executing in kernel space, then the trap entry code
will put ASI_P in %asi, and this will prevent copy_from_user() from
reading any useful stack data in either of the perf_callchain_user_X
functions, and thus no user callgraph data will be collected for this
sample period. An additional problem is that a fault is guaranteed
to occur, and though it will be silently covered up, it wastes time
and could perturb state.
In perf_callchain_user(), we ensure that %asi contains ASI_AIUS
because we know for a fact that the subsequent calls to
copy_from_user() are intended to read the user's stack.
Signed-off-by: Rob Gardner <rob.gardner@xxxxxxxxxx>
Signed-off-by: Dave Aldridge <david.j.aldridge@xxxxxxxxxx>
---
arch/sparc/kernel/perf_event.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/arch/sparc/kernel/perf_event.c b/arch/sparc/kernel/perf_event.c
index 689db65..55a6caa 100644
--- a/arch/sparc/kernel/perf_event.c
+++ b/arch/sparc/kernel/perf_event.c
@@ -1810,11 +1810,19 @@ static void perf_callchain_user_32(struct perf_callchain_entry *entry,
void
perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
{
+ u8 saved_asi;
+
perf_callchain_store(entry, regs->tpc);
if (!current->mm)
return;
+ /* ensure we get user memory when trying to read stacks */
+ __asm__ __volatile__ ("rd %%asi, %0\n" : "=r" (saved_asi));
+ if (saved_asi != ASI_AIUS)
+ __asm__ __volatile__ (
+ "wr %%g0, %0, %%asi\n" : : "i" (ASI_AIUS));
+
flushw_user();
pagefault_disable();
@@ -1825,4 +1833,8 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
perf_callchain_user_64(entry, regs);
pagefault_enable();
+
+ if (saved_asi != ASI_AIUS)
+ __asm__ __volatile__ (
+ "wr %%g0, %0, %%asi\n" : : "r" (saved_asi));
}
--
1.7.9.5
--
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