x86/xen/64: Rearrange the SYSCALL entries
Xen's raw SYSCALL entries are much less weird than native. Rather
than fudging them to look like native entries, use the Xen-provided
stack frame directly.
This lets us eliminate entry_SYSCALL_64_after_swapgs and two uses of
the SWAPGS_UNSAFE_STACK paravirt hook. The SYSENTER code would
benefit from similar treatment.
This makes one change to the native code path: the compat
instruction that clears the high 32 bits of %rax is moved slightly
later. I'd be surprised if this affects performance at all.
Tested-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/7c88ed36805d36841ab03ec3b48b4122c4418d71.1502164668.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/entry/entry_64_compat.S b/arch/x86/entry/entry_64_compat.S
index e1721da..5314d7b 100644
--- a/arch/x86/entry/entry_64_compat.S
+++ b/arch/x86/entry/entry_64_compat.S
@@ -183,21 +183,20 @@
*/
ENTRY(entry_SYSCALL_compat)
/* Interrupts are off on entry. */
- SWAPGS_UNSAFE_STACK
+ swapgs
/* Stash user ESP and switch to the kernel stack. */
movl %esp, %r8d
movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp
- /* Zero-extending 32-bit regs, do not remove */
- movl %eax, %eax
-
/* Construct struct pt_regs on stack */
pushq $__USER32_DS /* pt_regs->ss */
pushq %r8 /* pt_regs->sp */
pushq %r11 /* pt_regs->flags */
pushq $__USER32_CS /* pt_regs->cs */
pushq %rcx /* pt_regs->ip */
+GLOBAL(entry_SYSCALL_compat_after_hwframe)
+ movl %eax, %eax /* discard orig_ax high bits */
pushq %rax /* pt_regs->orig_ax */
pushq %rdi /* pt_regs->di */
pushq %rsi /* pt_regs->si */