Messages in this thread | | | Date | Sun, 14 Jan 2018 16:41:08 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH v2] x86/retpoline: Add LFENCE to the retpoline/RSB filling RSB macros |
| |
On Sat, Jan 13, 2018 at 05:27:30PM -0600, Tom Lendacky wrote: > The PAUSE instruction is currently used in the retpoline and RSB filling > macros as a speculation trap. The use of PAUSE was originally suggested > because it showed a very, very small difference in the amount of > cycles/time used to execute the retpoline as compared to LFENCE. On AMD, > the PAUSE instruction is not a serializing instruction, so the pause/jmp > loop will use excess power as it is speculated over waiting for return > to mispredict to the correct target. > > The RSB filling macro is applicable to AMD, and, if software is unable to > verify that LFENCE is serializing on AMD (possible when running under a > hypervisor), the generic retpoline support will be used and, so, is also > applicable to AMD. Keep the current usage of PAUSE for Intel, but add an > LFENCE instruction to the speculation trap for AMD. > > Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com> > --- > arch/x86/include/asm/nospec-branch.h | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-)
Reviewed-by: Borislav Petkov <bp@suse.de>
-- Regards/Gruss, Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
| |