[PATCH] KVM: MMU: Fix cmpxchg8b emulation

cmpxchg8b uses edx:eax as the compare operand, not edi:eax.

cmpxchg8b is used by 32-bit pae guests to set page table entries atomically,
and this is emulated touching shadowed guest page tables.

Also, implement it for 32-bit hosts.

Signed-off-by: Avi Kivity <avi@qumranet.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 28 insertions, 1 deletions

diff --git a/drivers/kvm/kvm_main.c b/drivers/kvm/kvm_main.c
index cec10106ce77..2e6bc5659953 100644
--- a/drivers/kvm/kvm_main.c
+++ b/drivers/kvm/kvm_main.c
@@ -936,6 +936,30 @@ static int emulator_cmpxchg_emulated(unsigned long addr,
         return emulator_write_emulated(addr, new, bytes, ctxt);
 }
 
+#ifdef CONFIG_X86_32
+
+static int emulator_cmpxchg8b_emulated(unsigned long addr,
+                                       unsigned long old_lo,
+                                       unsigned long old_hi,
+                                       unsigned long new_lo,
+                                       unsigned long new_hi,
+                                       struct x86_emulate_ctxt *ctxt)
+{
+        static int reported;
+        int r;
+
+        if (!reported) {
+                reported = 1;
+                printk(KERN_WARNING "kvm: emulating exchange8b as write\n");
+        }
+        r = emulator_write_emulated(addr, new_lo, 4, ctxt);
+        if (r != X86EMUL_CONTINUE)
+                return r;
+        return emulator_write_emulated(addr+4, new_hi, 4, ctxt);
+}
+
+#endif
+
 static unsigned long get_segment_base(struct kvm_vcpu *vcpu, int seg)
 {
         return kvm_arch_ops->get_segment_base(vcpu, seg);
@@ -1010,6 +1034,9 @@ struct x86_emulate_ops emulate_ops = {
         .read_emulated       = emulator_read_emulated,
         .write_emulated      = emulator_write_emulated,
         .cmpxchg_emulated    = emulator_cmpxchg_emulated,
+#ifdef CONFIG_X86_32
+        .cmpxchg8b_emulated  = emulator_cmpxchg8b_emulated,
+#endif
 };
 
 int emulate_instruction(struct kvm_vcpu *vcpu,
diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
index 1bff3e925fda..be70795b4822 100644
--- a/drivers/kvm/x86_emulate.c
+++ b/drivers/kvm/x86_emulate.c
@@ -1323,7 +1323,7 @@ twobyte_special_insn:
                                                          ctxt)) != 0))
                                 goto done;
                         if ((old_lo != _regs[VCPU_REGS_RAX])
-                            || (old_hi != _regs[VCPU_REGS_RDI])) {
+                            || (old_hi != _regs[VCPU_REGS_RDX])) {
                                 _regs[VCPU_REGS_RAX] = old_lo;
                                 _regs[VCPU_REGS_RDX] = old_hi;
                                 _eflags &= ~EFLG_ZF;