On Sun, Jul 6, 2008 at 10:51 AM, Avi Kivity <[EMAIL PROTECTED]> wrote:
> Mohammed Gamal wrote:
>>
>> This patch resolves the problem encountered with HLT emulation with
>> FreeDOS's HIMEM XMS Driver.
>> HLT is the only instruction that goes to the done label unconditionally,
>> causing the EIP value not to be updated which leads to the guest looping
>> forever on the same instruction.
>>
>> Signed-off-by: Mohammed Gamal <[EMAIL PROTECTED]>
>>
>> ---
>>
>> arch/x86/kvm/x86_emulate.c | 4 +++-
>> 1 files changed, 3 insertions(+), 1 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
>> index dd4efe1..04d7f02 100644
>> --- a/arch/x86/kvm/x86_emulate.c
>> +++ b/arch/x86/kvm/x86_emulate.c
>> @@ -1769,13 +1769,15 @@ writeback:
>> /* Commit shadow register state. */
>> memcpy(ctxt->vcpu->arch.regs, c->regs, sizeof c->regs);
>> - kvm_rip_write(ctxt->vcpu, c->eip);
>> done:
>> if (rc == X86EMUL_UNHANDLEABLE) {
>> c->eip = saved_eip;
>> return -1;
>> }
>> + else
>> + kvm_rip_write(ctxt->vcpu, c->eip);
>> +
>> return 0;
>
> Why not change hlt to writeback like all other instructions?
>
IIRC hlt doesn't do writebacks. So, instead of changing hlt to go for
a bogus writeback, I thought it'd be more logical that since we're
going to the done label anyway we check first if the instruction is
unhandleable, in which case we write the saved EIP, otherwise we
update the EIP value.
Anyway, here is a patch that changes hlt to writeback.
arch/x86/kvm/x86_emulate.c | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)
diff --git a/arch/x86/kvm/x86_emulate.c b/arch/x86/kvm/x86_emulate.c
index dd4efe1..62e71b6 100644
--- a/arch/x86/kvm/x86_emulate.c
+++ b/arch/x86/kvm/x86_emulate.c
@@ -1732,7 +1732,7 @@ special_insn:
break;
case 0xf4: /* hlt */
ctxt->vcpu->arch.halt_request = 1;
- goto done;
+ break;
case 0xf5: /* cmc */
/* complement carry flag from eflags reg */
ctxt->eflags ^= EFLG_CF;
