From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CB844C43381 for ; Tue, 5 Mar 2019 11:51:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 98CB9206DD for ; Tue, 5 Mar 2019 11:51:18 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727982AbfCELvR (ORCPT ); Tue, 5 Mar 2019 06:51:17 -0500 Received: from foss.arm.com ([217.140.101.70]:47414 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727424AbfCELvQ (ORCPT ); Tue, 5 Mar 2019 06:51:16 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 50A85A78; Tue, 5 Mar 2019 03:51:16 -0800 (PST) Received: from [10.1.196.92] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 805AA3F71D; Tue, 5 Mar 2019 03:51:14 -0800 (PST) Subject: Re: [RFC PATCH] KVM: arm64: Force a PTE mapping when logging is enabled To: Zenghui Yu , Suzuki K Poulose , Zenghui Yu Cc: christoffer.dall@arm.com, Punit Agrawal , julien.thierry@arm.com, LKML , james.morse@arm.com, wanghaibin.wang@huawei.com, kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org References: <1551497728-12576-1-git-send-email-yuzenghui@huawei.com> <20190304171320.GA3984@en101> <32f302eb-ef89-7de4-36b4-3c3df907c732@arm.com> <865b8b0b-e42e-fe03-e3b4-ae2cc5b1b424@huawei.com> From: Marc Zyngier Openpgp: preference=signencrypt Autocrypt: addr=marc.zyngier@arm.com; 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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <865b8b0b-e42e-fe03-e3b4-ae2cc5b1b424@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 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 */ > > 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... 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Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1h18bQ-0005wp-ST; Tue, 05 Mar 2019 11:51:20 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1h18bM-0005vV-V6 for linux-arm-kernel@lists.infradead.org; Tue, 05 Mar 2019 11:51:18 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 50A85A78; Tue, 5 Mar 2019 03:51:16 -0800 (PST) Received: from [10.1.196.92] (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 805AA3F71D; Tue, 5 Mar 2019 03:51:14 -0800 (PST) Subject: Re: [RFC PATCH] KVM: arm64: Force a PTE mapping when logging is enabled To: Zenghui Yu , Suzuki K Poulose , Zenghui Yu References: <1551497728-12576-1-git-send-email-yuzenghui@huawei.com> <20190304171320.GA3984@en101> <32f302eb-ef89-7de4-36b4-3c3df907c732@arm.com> <865b8b0b-e42e-fe03-e3b4-ae2cc5b1b424@huawei.com> From: Marc Zyngier Openpgp: preference=signencrypt Autocrypt: addr=marc.zyngier@arm.com; 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Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <865b8b0b-e42e-fe03-e3b4-ae2cc5b1b424@huawei.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190305_035117_016662_81FEDD37 X-CRM114-Status: GOOD ( 21.34 ) 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, 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 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 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 */ > > 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... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel