Commit 987c4263 authored by Nicholas Piggin's avatar Nicholas Piggin Committed by Michael Ellerman
Browse files

powerpc/64s/perf: perf interrupt does not have to get_user_pages to access user memory 



read_user_stack_slow that walks user address translation by hand is
only required on hash, because a hash fault can not be serviced from
"NMI" context (to avoid re-entering the hash code) so the user stack
can be mapped into Linux page tables but not accessible by the CPU.

Radix MMU mode does not have this restriction. A page fault failure
would indicate the page is not accessible via get_user_pages either,
so avoid this on radix.

Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201111120151.3150658-1-npiggin@gmail.com
parent fdcfeaba

arch/powerpc/perf/callchain.h

+1 −1
Original line number Diff line number Diff line
@@ -33,7 +33,7 @@ static inline int __read_user_stack(const void __user *ptr, void *ret, 


	rc = copy_from_user_nofault(ret, ptr, size);



	if (IS_ENABLED(CONFIG_PPC64) && rc)

	if (IS_ENABLED(CONFIG_PPC64) && !radix_enabled() && rc)

		return read_user_stack_slow(ptr, ret, size);



	return rc;

arch/powerpc/perf/callchain_64.c

+2 −1
Original line number Diff line number Diff line
@@ -21,7 +21,8 @@ 
/*

 * On 64-bit we don't want to invoke hash_page on user addresses from

 * interrupt context, so if the access faults, we read the page tables

 * to find which page (if any) is mapped and access it directly.

 * to find which page (if any) is mapped and access it directly. Radix

 * has no need for this so it doesn't use read_user_stack_slow.

 */

int read_user_stack_slow(const void __user *ptr, void *buf, int nb)

{