[Xen-devel] Re: [GIT PULL] xen /proc/mtrr implementation

["H. Peter Anvin" <hpa@xxxxxxxxx>]

Andi Kleen wrote:
>>> Is this new interface only defined for swiotlb or MMIO mappings?
>>> If yes did you check the drivers only actually set it on
>>> swiotlb or MMIO (that seems dubious to me)?
>> Really?   Do we ever set unusual memory types on normal system memory?  
> 
> There were drivers at some point that set WC MTRRs on their
> transfer rings, not mmio.
> 
> Maybe these all switched to PAT now, maybe not

Most of those that I've heard of use WB memory and CLFLUSH.

The ones I know of which marked descriptor rings WB were ones which had
descriptor rings in MMIO space (which makes sense: MMIO reads are fully
synchronizing, but writes can be posted and write combined.)

        -hpa


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