Re: [PATCH 0/6] MTRR/PAT support for EPT (v3)

[Avi Kivity <avi@redhat.com>]

Sheng Yang wrote:
> On Thursday 09 October 2008 17:03:24 Avi Kivity wrote:
>   
>> Sheng Yang wrote:
>>     
>>> Hi, Avi
>>>
>>> Here is the latest update of MTRR/PAT support.
>>>
>>> Change from v2:
>>> Discard the using of MSR bitmap, add MSR_IA32_CR_PAT to save/restore, as
>>> well as rebase on latest upstream.
>>>       
>> Applied all; my comments about shadow can be addressed later.
>>
>> There is also the danger of the guest setting the wrong MTRR type for
>> RAM, thus introducing incompatible memory types (between qemu and the
>> guest).  If this is a problem, we should ignore the guest's mtrr (and
>> pat) for RAM and use write-back instead.
>>     
>
> Do you mean host(qemu) would access this memory and if we set it to guest 
> MTRR, host access would be broken? We would cover this in our shadow MTRR 
> patch, for we encountered this in video ram when doing some experiment with 
> VGA assignment. 
>   

No, I think that the cpu requires that all accesses to a page be done
using the same memory type.  We are allowing the guest to break that,
since qemu mappings will use writeback and guest mapping will use guest
specified memory types.

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