From: Keir Fraser <keir@xensource.com>
Date: Mon, 15 Oct 2007 11:13:41 +0000 (+0100)
Subject: x86/64: Do not clobber %r11 (user rflags) on syscall from guest
X-Git-Tag: 3.2.0-rc1~228^2~36
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=b28b3c245ac495e87da7303954e2a1350dc6dd9d;p=xen.git

x86/64: Do not clobber %r11 (user rflags) on syscall from guest
userspace to guest kernel. The flags are saved on the guest kernel
stack anyway, but some guests rely on %r11 instead.
Signed-off-by: Keir Fraser <keir@xensource.com>
---

diff --git a/xen/arch/x86/x86_64/entry.S b/xen/arch/x86/x86_64/entry.S
index ad9e9ceebc..ca67151e0b 100644
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -106,7 +106,7 @@ restore_all_xen:
  * When entering SYSCALL from kernel mode:
  *  %rax                            = hypercall vector
  *  %rdi, %rsi, %rdx, %r10, %r8, %9 = hypercall arguments
- *  %r11, %rcx                      = SYSCALL-saved %rflags and %rip
+ *  %rcx                            = SYSCALL-saved %rip
  *  NB. We must move %r10 to %rcx for C function-calling ABI.
  *
  * When entering SYSCALL from user mode:
@@ -125,6 +125,7 @@ ENTRY(syscall_enter)
         pushq %rcx
         pushq $0
         movl  $TRAP_syscall,4(%rsp)
+        movq  24(%rsp),%r11 /* Re-load user RFLAGS into %r11 before SAVE_ALL */
         SAVE_ALL
         GET_CURRENT(%rbx)
         testb $TF_kernel_mode,VCPU_thread_flags(%rbx)