This is a note to let you know that I've just added the patch titled
powerpc: Avoid taking a data miss on every userspace instruction miss
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: powerpc-avoid-taking-a-data-miss-on-every-userspace-instruction-miss.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Sun Mar 18 16:55:33 CET 2018
From: Anton Blanchard anton@samba.org Date: Mon, 3 Apr 2017 16:41:02 +1000 Subject: powerpc: Avoid taking a data miss on every userspace instruction miss
From: Anton Blanchard anton@samba.org
[ Upstream commit a7a9dcd882a67b68568868b988289fce5ffd8419 ]
Early on in do_page_fault() we call store_updates_sp(), regardless of the type of exception. For an instruction miss this doesn't make sense, because we only use this information to detect if a data miss is the result of a stack expansion instruction or not.
Worse still, it results in a data miss within every userspace instruction miss handler, because we try and load the very instruction we are about to install a pte for!
A simple exec microbenchmark runs 6% faster on POWER8 with this fix:
#include <stdlib.h> #include <stdio.h> #include <unistd.h>
int main(int argc, char *argv[]) { unsigned long left = atol(argv[1]); char leftstr[16];
if (left-- == 0) return 0;
sprintf(leftstr, "%ld", left); execlp(argv[0], argv[0], leftstr, NULL); perror("exec failed\n");
return 0; }
Pass the number of iterations on the command line (eg 10000) and time how long it takes to execute.
Signed-off-by: Anton Blanchard anton@samba.org Signed-off-by: Michael Ellerman mpe@ellerman.id.au Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/powerpc/mm/fault.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/powerpc/mm/fault.c +++ b/arch/powerpc/mm/fault.c @@ -294,7 +294,7 @@ int do_page_fault(struct pt_regs *regs, * can result in fault, which will cause a deadlock when called with * mmap_sem held */ - if (user_mode(regs)) + if (!is_exec && user_mode(regs)) store_update_sp = store_updates_sp(regs);
if (user_mode(regs))
Patches currently in stable-queue which might be from anton@samba.org are
queue-4.9/powerpc-avoid-taking-a-data-miss-on-every-userspace-instruction-miss.patch