Re: KVM: x86: Push potential exception error code on task switches

[Jan Kiszka <jan.kiszka@siemens.com>]

Avi Kivity wrote:
> On 04/14/2010 03:37 PM, Jan Kiszka wrote:
>> Avi Kivity wrote:
>>    
>>> On 04/14/2010 03:11 PM, Jan Kiszka wrote:
>>>      
>>>> When a fault triggers a task switch, the error code, if it exists, has
>>>> to be pushed on the new task's stack. Implement the missing bits.
>>>>
>>>>
>>>> @@ -2416,12 +2417,23 @@ static int emulator_do_task_switch(struct x86_emulate_ctxt *ctxt,
>>>>    	ops->set_cached_descriptor(&next_tss_desc, VCPU_SREG_TR, ctxt->vcpu);
>>>>    	ops->set_segment_selector(tss_selector, VCPU_SREG_TR, ctxt->vcpu);
>>>>
>>>> +	if (ret == X86EMUL_CONTINUE&&   has_error_code) {
>>>> +		struct decode_cache *c =&ctxt->decode;
>>>> +
>>>> +		c->op_bytes = c->ad_bytes = (next_tss_desc.type&   8) ? 4 : 2;
>>>>
>>>>        
>>> Don't these depend on the attributes of the segment as well?
>>>      
>> Not on the segment, but actually on the gate size. Will fix.
>>    
> 
> The TSS descriptor (gate doesn't have a size).  But isn't it possible to 
> have a 32-bit TSS with a 16-bit CS/SS?

Might be possible, but will cause troubles as the spec says:

"The error code is pushed on the stack as a doubleword or word
(depending on the default interrupt, trap, or task gate size)."

Jan

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