From: Denys Vlasenko Date: Thu, 19 Mar 2015 17:17:47 +0000 (+0100) Subject: x86/asm/entry/64: Use PUSH instructions to build pt_regs on stack X-Git-Tag: omap-for-v4.1/fixes-rc1~195^2~61 X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9ed8e7d86061e7c3fb3855358d51ba4abb19ceb1;p=pandora-kernel.git x86/asm/entry/64: Use PUSH instructions to build pt_regs on stack With this change, on SYSCALL64 code path we are now populating pt_regs->cs, pt_regs->ss and pt_regs->rcx unconditionally and therefore don't need to do that in FIXUP_TOP_OF_STACK. We lose a number of large instructions there: text data bss dec hex filename 13298 0 0 13298 33f2 entry_64_before.o 12978 0 0 12978 32b2 entry_64.o What's more important, we convert two "MOVQ $imm,off(%rsp)" to "PUSH $imm" (the ones which fill pt_regs->cs,ss). Before this patch, placing them on fast path was slowing it down by two cycles: this form of MOV is very large, 12 bytes, and this probably reduces decode bandwidth to one instruction per cycle when CPU sees them. Therefore they were living in FIXUP_TOP_OF_STACK instead (away from fast path). "PUSH $imm" is a small 2-byte instruction. Moving it to fast path does not slow it down in my measurements. Signed-off-by: Denys Vlasenko Acked-by: Borislav Petkov Acked-by: Andy Lutomirski Cc: Alexei Starovoitov Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Frederic Weisbecker Cc: H. Peter Anvin Cc: Kees Cook Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Steven Rostedt Cc: Will Drewry Link: http://lkml.kernel.org/r/1426785469-15125-3-git-send-email-dvlasenk@redhat.com Signed-off-by: Ingo Molnar --- Reading git-diff-tree failed