On 05/03/2019 11:09, Zenghui Yu wrote: > Hi Marc, Suzuki, > > On 2019/3/5 1:34, Marc Zyngier wrote: >> Hi Zenghui, Suzuki, >> >> On 04/03/2019 17:13, Suzuki K Poulose wrote: >>> 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 */ > > A nicer implementation and easier to understand, thanks! > >> That's pretty interesting, because this is almost what we already have >> in the NV code: >> >> https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/tree/virt/kvm/arm/mmu.c?h=kvm-arm64/nv-wip-v5.0-rc7#n1752 >> >> (note that force_pte is gone in that branch). > > haha :-) sorry about that. I haven't looked into the NV code yet, so ... > > But I'm still wondering: should we fix this wrong mapping size problem > before NV is introduced? Since this problem has not much to do with NV, > and 5.0 has already been released with this problem (and 5.1 will > without fix ...). > > Just a personal idea, ignore it if unnecessary. We definitely want to fix it now, and have the fix backported to older versions. I can always rebase the NV branch on top of the current state of mainline. Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
