I think there're still some problems in this patch... Details below. On Sat, Mar 2, 2019 at 11:39 AM Zenghui Yu <yuzenghui@xxxxxxxxxx> wrote: > > The idea behind this is: we don't want to keep tracking of huge pages when > logging_active is true, which will result in performance degradation. We > still need to set vma_pagesize to PAGE_SIZE, so that we can make use of it > to force a PTE mapping. > > Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx> > Cc: Punit Agrawal <punit.agrawal@xxxxxxx> > Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx> > > --- > Atfer looking into https://patchwork.codeaurora.org/patch/647985/ , the > "vma_pagesize = PAGE_SIZE" logic was not intended to be deleted. As far > as I can tell, we used to have "hugetlb" to force the PTE mapping, but > we have "vma_pagesize" currently instead. We should set it properly for > performance reasons (e.g, in VM migration). Did I miss something important? > > --- > virt/kvm/arm/mmu.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c > index 30251e2..7d41b16 100644 > --- a/virt/kvm/arm/mmu.c > +++ b/virt/kvm/arm/mmu.c > @@ -1705,6 +1705,13 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > (vma_pagesize == PUD_SIZE && kvm_stage2_has_pmd(kvm))) && > !force_pte) { > gfn = (fault_ipa & huge_page_mask(hstate_vma(vma))) >> PAGE_SHIFT; > + } else { > + /* > + * Fallback to PTE if it's not one of the stage2 > + * supported hugepage sizes or the corresponding level > + * doesn't exist, or logging is enabled. First, Instead of "logging is enabled", it should be "force_pte is true", since "force_pte" will be true when: 1) fault_supports_stage2_pmd_mappings() return false; or 2) "logging is enabled" (e.g, in VM migration). Second, fallback some unsupported hugepage sizes (e.g, 64K hugepage with 4K pages) to PTE is somewhat strange. And it will then _unexpectedly_ reach transparent_hugepage_adjust(), though no real adjustment will happen since commit fd2ef358282c ("KVM: arm/arm64: Ensure only THP is candidate for adjustment"). Keeping "vma_pagesize" there as it is will be better, right? So I'd just simplify the logic like: } else if (force_pte) { vma_pagesize = PAGE_SIZE; } Will send a V2 later and waiting for your comments :) thanks, zenghui > + */ > + vma_pagesize = PAGE_SIZE; > } > up_read(¤t->mm->mmap_sem); > > -- > 1.8.3.1 > > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
