Messages in this thread | | | Date | Sun, 29 Mar 2009 16:15:07 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH 4/7] kvm mmu: implement necessary data structures for second huge page accounting |
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Joerg Roedel wrote: >> >>> +static int has_wrprotected_largepage(struct kvm *kvm, gfn_t gfn) >>> +{ >>> + struct kvm_memory_slot *slot; >>> + int *hugepage_idx; >>> + >>> + gfn = unalias_gfn(kvm, gfn); >>> + slot = gfn_to_memslot_unaliased(kvm, gfn); >>> + if (slot) { >>> + hugepage_idx = slot_hugepage_idx(gfn, slot); >>> >>> >> slot_largepage_idx() here? >> >> I don't think we ever write protect large pages, so why is this needed? >> > > For 2mb pages we need to check if there is a write-protected 4k page in it > before we map a 2mb page for writing. If there is any write-protected 4k > page in a 2mb area this 2mb page is considered write-protected. These > 'write-protected' 2mb pages are accounted in the account_shadow() > function. This information is taken into account when we decide if we > can map a guest 1gb page as a 1gb page on the host too. >
account_shadowed() actually increments a hugepage write_count by 1 for every 4K page, not 2M page, if I read the code correctly. The code I commented on is right though.
The naming is confusing. I suggest has_wrprotected_page_in_{large,huge}page(). although with the a level parameter we can keep has_wrprotected_page().
btw, if we implement account_shadow() as you describe it (only account hugepages on largepage transition 0->1 or 1->0) we save a potential cacheline bounce on the hugepage write_count accounting array.
-- error compiling committee.c: too many arguments to function
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