Re: [PATCH v3] x86/hvmloader: select xenpci MMIO BAR UC or WB MTRR cache attribute

["Tu Dinh" <ngoc-tu.dinh@xxxxxxxxxx>]

On 06/06/2025 15:23, Roger Pau Monné wrote:
[...]
>>
>> Since this is meant to be a workaround, I wonder if it makes more sense
>> to flip the setting (`xenpci_bar_wb`) and make it 0 by default?
>
> I originally didn't want to go that route, because while it's true
> that the default MTRR type is set to WB, and so any memory not covered
> by a MTRR range will default to that memory type I got the impression
> this was inferring too much.
>
> Overall my intention would be for inverting the default long term, and
> libxl setting build_info->u.hvm.xenpci_bar_uc = false by default,
> which then makes all the naming nicer IMO.
>
>> It also
>> simplifies the logic for both hvmloader and the consumer (no need for
>> double negatives).
>
> I don't think there are double negatives?  That would happen if the
> variable was named xenpci_bar_no_uc or similar?

It's because from the flag consumer's viewpoint, I saw the flag
`xenpci_bar_uc` as rather "xenpci_bar_dont_apply_wb_workaround`. But if
the intention is to eventually make it default then the naming is OK for me.

>
> Thanks, Roger.




Ngoc Tu Dinh | Vates XCP-ng Developer

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