Re: [PATCH v3 7/7] mm/memremap: Set caching mode for PCI P2PDMA memory to WC

Logan Gunthorpe
2020-03-02T21:20:07Z

On 2020-02-29 3:47 p.m., Dan Williams wrote:
> On Fri, Feb 21, 2020 at 10:25 AM Logan Gunthorpe <logang@deltatee.com> wrote:
>>
>> PCI BAR IO memory should never be mapped as WB, however prior to this
>> the PAT bits were set WB and it was typically overridden by MTRR
>> registers set by the firmware.
>>
>> Set PCI P2PDMA memory to be WC (writecombining) as the only current
>> user (the NVMe CMB) was originally mapped WC before the P2PDMA code
>> replaced the mapping with devm_memremap_pages().
>
> Will the change to UC regress this existing use case?

I don't think so. They've been essentially mapped UC for a long time now
(since the P2PDMA patch set was merged) and nobody has complained.