On 22.12.2022 11:00, Demi Marie Obenour wrote: > On Thu, Dec 22, 2022 at 10:54:48AM +0100, Jan Beulich wrote: >> On 22.12.2022 10:50, Demi Marie Obenour wrote: >>> On Thu, Dec 22, 2022 at 10:35:08AM +0100, Jan Beulich wrote: >>>> On 20.12.2022 02:07, Demi Marie Obenour wrote: >>>>> @@ -6361,6 +6366,72 @@ static void __init __maybe_unused >>>>> build_assertions(void) >>>>> * using different PATs will not work. >>>>> */ >>>>> BUILD_BUG_ON(XEN_MSR_PAT != 0x050100070406ULL); >>>>> + >>>>> + /* >>>>> + * _PAGE_WB must be zero for several reasons, not least because Linux >>>>> + * assumes it. >>>>> + */ >>>>> + BUILD_BUG_ON(_PAGE_WB); >>>> >>>> Strictly speaking this is a requirement only for PV guests. We may not >>>> want to go as far as putting "#ifdef CONFIG_PV" around it, but at least >>>> the code comment (and then also the part of the description referring >>>> to this) will imo want to say so. >>> >>> Does Xen itself depend on this? >> >> With the wording in the description I was going from the assumption that >> you have audited code and found that we properly use _PAGE_* constants >> everywhere. > > There could be other hard-coded uses of magic numbers I haven’t found, > and _PAGE_WB is currently zero so I would be quite surpised if no code > in Xen omits it. Linux also has a BUILD_BUG_ON() to check the same > thing.
Fair enough - please adjust description and comment text accordingly then. Jan
