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 <yuzeng...@huawei.com> 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.poul...@arm.com> >>> Cc: Punit Agrawal <punit.agra...@arm.com> >>> Signed-off-by: Zenghui Yu <yuzeng...@huawei.com> >>> >>> --- >>> 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 */ 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). Thanks, M. -- Jazz is not dead. It just smells funny...
