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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190304171320.GA3984@en101> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190304_093414_002731_E00C9C9F X-CRM114-Status: GOOD ( 24.52 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: julien.thierry@arm.com, Punit Agrawal , LKML , christoffer.dall@arm.com, james.morse@arm.com, Zenghui Yu , wanghaibin.wang@huawei.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 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 >>> Cc: Punit Agrawal >>> Signed-off-by: Zenghui Yu >>> >>> --- >>> 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... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel