Hi Zenghui, On Sun, Mar 03, 2019 at 11:14:38PM +0800, Zenghui Yu wrote: > 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. Yes, you're right. We are indeed ignoring the force_pte flag. > > > > 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: We could fix this right in the beginning. See patch below: > > } else if (force_pte) { > vma_pagesize = PAGE_SIZE; > } > > > Will send a V2 later and waiting for your comments :) diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c index 30251e2..529331e 100644 --- a/virt/kvm/arm/mmu.c +++ b/virt/kvm/arm/mmu.c @@ -1693,7 +1693,9 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, return -EFAULT; } - vma_pagesize = vma_kernel_pagesize(vma); + /* If we are forced to map at page granularity, force the pagesize here */ + vma_pagesize = force_pte ? PAGE_SIZE : vma_kernel_pagesize(vma); + /* * The stage2 has a minimum of 2 level table (For arm64 see * kvm_arm_setup_stage2()). Hence, we are guaranteed that we can @@ -1701,11 +1703,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, * As for PUD huge maps, we must make sure that we have at least * 3 levels, i.e, PMD is not folded. */ - if ((vma_pagesize == PMD_SIZE || - (vma_pagesize == PUD_SIZE && kvm_stage2_has_pmd(kvm))) && - !force_pte) { + if (vma_pagesize == PMD_SIZE || + (vma_pagesize == PUD_SIZE && kvm_stage2_has_pmd(kvm))) gfn = (fault_ipa & huge_page_mask(hstate_vma(vma))) >> PAGE_SHIFT; - } + up_read(¤t->mm->mmap_sem); /* We need minimum second+third level pages */ --- Suzuki _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
