From 98f05b5138f0a9b56022295cc1387e635b25635d Mon Sep 17 00:00:00 2001 From: Andy Lutomirski Date: Mon, 3 Sep 2018 15:59:43 -0700 Subject: x86/entry/64: Use the TSS sp2 slot for SYSCALL/SYSRET scratch space In the non-trampoline SYSCALL64 path, a percpu variable is used to temporarily store the user RSP value. Instead of a separate variable, use the otherwise unused sp2 slot in the TSS. This will improve cache locality, as the sp1 slot is already used in the same code to find the kernel stack. It will also simplify a future change to make the non-trampoline path work in PTI mode. Signed-off-by: Andy Lutomirski Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov Cc: Borislav Petkov Cc: Dave Hansen Cc: Adrian Hunter Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Linus Torvalds Cc: Josh Poimboeuf Cc: Joerg Roedel Cc: Jiri Olsa Cc: Andi Kleen Cc: Peter Zijlstra Link: https://lkml.kernel.org/r/08e769a0023dbad4bac6f34f3631dbaf8ad59f4f.1536015544.git.luto@kernel.org --- arch/x86/xen/xen-asm_64.S | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'arch/x86/xen') diff --git a/arch/x86/xen/xen-asm_64.S b/arch/x86/xen/xen-asm_64.S index 417b339e5c8e..bb1c2da0381d 100644 --- a/arch/x86/xen/xen-asm_64.S +++ b/arch/x86/xen/xen-asm_64.S @@ -91,13 +91,15 @@ ENTRY(xen_iret) ENTRY(xen_sysret64) /* * We're already on the usermode stack at this point, but - * still with the kernel gs, so we can easily switch back + * still with the kernel gs, so we can easily switch back. + * + * tss.sp2 is scratch space. */ - movq %rsp, PER_CPU_VAR(rsp_scratch) + movq %rsp, PER_CPU_VAR(cpu_tss_rw + TSS_sp2) movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp pushq $__USER_DS - pushq PER_CPU_VAR(rsp_scratch) + pushq PER_CPU_VAR(cpu_tss_rw + TSS_sp2) pushq %r11 pushq $__USER_CS pushq %rcx -- cgit