[PATCH 26/33] KVM: MMU: Fix cmpxchg8b emulation

Avi Kivity
2007-01-04T16:15:07Z

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-atKUWr5tajBWk0Htik3J/w@public.gmane.org>

Index: linux-2.6/drivers/kvm/x86_emulate.c
===================================================================
--- linux-2.6.orig/drivers/kvm/x86_emulate.c
+++ linux-2.6/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;
Index: linux-2.6/drivers/kvm/kvm_main.c
===================================================================
--- linux-2.6.orig/drivers/kvm/kvm_main.c
+++ linux-2.6/drivers/kvm/kvm_main.c
@@ -936,6 +936,30 @@ static int emulator_cmpxchg_emulated(uns
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,