Re: [PATCH] EFI: Only set regions uncacheable if they support it

["H. Peter Anvin" <hpa@zytor.com>]

On 03/15/2012 07:24 AM, Matthew Garrett wrote:
> On Thu, Mar 15, 2012 at 07:17:56AM -0700, H. Peter Anvin wrote:
>> On 03/15/2012 07:07 AM, Matthew Garrett wrote:
>>>
>>> I have a report of a system that fails to boot with an MCE during EFI 
>>> setup. The memory range is marked reserved and claims not to support any 
>>> caching type, which I think probably translates as "Don't do anything to 
>>> this region ever".
>>>
>>
>> In other words, "don't map me"... not something we really support at the
>> moment, but perhaps we should; at least until we find systems in the
>> field that break with that constraint :(
> 
> Mapping should be harmless as long as we then don't touch it? I can't 
> think of any circumstances where we would.
> 

If we map it WB software can do speculative loads from that region which
would bring it into the cache.  If we map it UC we might have to CLFLUSH...

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.