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 <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/08e769a0023dbad4bac6f34f3631dbaf8ad59f4f.1536015544.git.luto@kernel.org
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index d53c54b..b2bb1d6 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -315,7 +315,13 @@ struct x86_hw_tss {
*/
u64 sp1;
+ /*
+ * Since Linux does not use ring 2, the 'sp2' slot is unused by
+ * hardware. entry_SYSCALL_64 uses it as scratch space to stash
+ * the user RSP value.
+ */
u64 sp2;
+
u64 reserved2;
u64 ist[7];
u32 reserved3;