On Thu, Oct 29, 2020 at 08:08:48AM +0100, Paolo Bonzini wrote: > On 28/10/20 16:29, Sean Christopherson wrote: > > The naming and usage also aligns with the kernel, which defines PAGE, PMD and > > PUD masks, and has near identical usage patterns. > > > > #define PAGE_SIZE (_AC(1,UL) << PAGE_SHIFT) > > #define PAGE_MASK (~(PAGE_SIZE-1)) > > > > #define PMD_PAGE_SIZE (_AC(1, UL) << PMD_SHIFT) > > #define PMD_PAGE_MASK (~(PMD_PAGE_SIZE-1)) > > > > #define PUD_PAGE_SIZE (_AC(1, UL) << PUD_SHIFT) > > #define PUD_PAGE_MASK (~(PUD_PAGE_SIZE-1)) > > Well, PAGE_MASK is also one of my pet peeves for Linux. At least I am > consistent. :) > > >> and of course if you're debugging it you have to > >> look closer and check if it's really "x & -y" or "x & ~y", but at least > >> in normal cursory code reading that's how it works for me. > > > > IMO, "x & -y" has a higher barrier to entry, especially when the kernel's page > > masks uses "x & ~(y - 1))". But, my opinion is definitely colored by my > > inability to read two's-complement on the fly. > > Fair enough. What about having instead > > #define KVM_HPAGE_GFN_BASE(gfn, level) \ > (x & ~(KVM_PAGES_PER_HPAGE(gfn) - 1)) > #define KVM_HPAGE_GFN_INDEX(gfn, level) \ > (x & (KVM_PAGES_PER_HPAGE(gfn) - 1)) > > ? Hmm, not awful? What about OFFSET instead of INDEX, to pair with page offset? I don't particularly love either one, but I can't think of anything better.
