Re: KVM: Fix the invlpg instruction emulation on AMD64

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Aurelien Jarno wrote:
>>> diff --git a/drivers/kvm/x86_emulate.c b/drivers/kvm/x86_emulate.c
>>> index e974ace..06e183b 100644
>>> --- a/drivers/kvm/x86_emulate.c
>>> +++ b/drivers/kvm/x86_emulate.c
>>> @@ -825,12 +825,12 @@ modrm_done:
>>>  		c->src.bytes = 4;
>>>  		goto srcmem_common;
>>>  	case SrcMem:
>>> -		c->src.bytes = (c->d & ByteOp) ? 1 :
>>> -							   c->op_bytes;
>>>  		/* Don't fetch the address for invlpg: it could be unmapped. */
>>> -		if (c->twobyte && c->b == 0x01
>>> -				    && c->modrm_reg == 7)
>>> +		if ((c->d & ModRM) && c->modrm_mod == 3) {
>>> +			c->src.type = OP_REG;
>>>  			break;
>>> +		}
>>> +		c->src.bytes = (c->d & ByteOp) ? 1 : c->op_bytes;
>>>  srcmem_common:
>>>  		c->src.type = OP_MEM;
>>>  		break;
>>>   
>>>       
>> Why did you remove the check for invlpg?  It need not be executed with
>> modrm_mod == 3 (in fact invlpg with modrm_mod == 3 is useless), so it
>> won't be caught by this.
>>     
>
> Because I really thing this check is buggy. On my tests, modrm_reg is
> always different than 7 for the invlpg instruction, so the test is
> always false.
>
>   


But invlpg is defined as having reg == 7! The manual says:

0F 01/7 INVLPG m

where "/7" is the notation for "reg in the mod reg r/m byte:

" /digit — A digit between 0 and 7 indicates that the ModR/M byte of the
instruction uses
only the r/m (register or memory) operand. The reg field contains the
digit that provides an
extension to the instruction's opcode."


So what you're seeing is not the invlpg instruction but something else
in the same group.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


-------------------------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc.
Still grepping through log files to find problems?  Stop.
Now Search log events and configuration files using AJAX and a browser.
Download your FREE copy of Splunk now >> http://get.splunk.com/