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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 autolearn=unavailable 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 65E59C433B4 for ; Wed, 7 Apr 2021 15:35:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 33BE46113A for ; Wed, 7 Apr 2021 15:35:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233287AbhDGPff (ORCPT ); Wed, 7 Apr 2021 11:35:35 -0400 Received: from foss.arm.com ([217.140.110.172]:59356 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230248AbhDGPfd (ORCPT ); Wed, 7 Apr 2021 11:35:33 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 470861424; Wed, 7 Apr 2021 08:35:23 -0700 (PDT) Received: from [192.168.0.110] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 402603F792; Wed, 7 Apr 2021 08:35:21 -0700 (PDT) Subject: Re: [RFC PATCH v3 2/2] KVM: arm64: Distinguish cases of memcache allocations completely To: Yanan Wang , Marc Zyngier , Will Deacon , Catalin Marinas , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Cc: James Morse , Julien Thierry , Suzuki K Poulose , Gavin Shan , Quentin Perret , wanghaibin.wang@huawei.com, zhukeqian1@huawei.com, yuzenghui@huawei.com References: <20210326031654.3716-1-wangyanan55@huawei.com> <20210326031654.3716-3-wangyanan55@huawei.com> From: Alexandru Elisei Message-ID: <4348b555-2a38-6f00-8ef0-0d5fd801d753@arm.com> Date: Wed, 7 Apr 2021 16:35:55 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.9.0 MIME-Version: 1.0 In-Reply-To: <20210326031654.3716-3-wangyanan55@huawei.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Yanan, On 3/26/21 3:16 AM, Yanan Wang wrote: > With a guest translation fault, the memcache pages are not needed if KVM > is only about to install a new leaf entry into the existing page table. > And with a guest permission fault, the memcache pages are also not needed > for a write_fault in dirty-logging time if KVM is only about to update > the existing leaf entry instead of collapsing a block entry into a table. > > By comparing fault_granule and vma_pagesize, cases that require allocations > from memcache and cases that don't can be distinguished completely. > > Signed-off-by: Yanan Wang > --- > arch/arm64/kvm/mmu.c | 25 ++++++++++++------------- > 1 file changed, 12 insertions(+), 13 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 1eec9f63bc6f..05af40dc60c1 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -810,19 +810,6 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > gfn = fault_ipa >> PAGE_SHIFT; > mmap_read_unlock(current->mm); > > - /* > - * Permission faults just need to update the existing leaf entry, > - * and so normally don't require allocations from the memcache. The > - * only exception to this is when dirty logging is enabled at runtime > - * and a write fault needs to collapse a block entry into a table. > - */ > - if (fault_status != FSC_PERM || (logging_active && write_fault)) { > - ret = kvm_mmu_topup_memory_cache(memcache, > - kvm_mmu_cache_min_pages(kvm)); > - if (ret) > - return ret; > - } > - > mmu_seq = vcpu->kvm->mmu_notifier_seq; > /* > * Ensure the read of mmu_notifier_seq happens before we call > @@ -880,6 +867,18 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > else if (cpus_have_const_cap(ARM64_HAS_CACHE_DIC)) > prot |= KVM_PGTABLE_PROT_X; > > + /* > + * Allocations from the memcache are required only when granule of the > + * lookup level where the guest fault happened exceeds vma_pagesize, > + * which means new page tables will be created in the fault handlers. > + */ > + if (fault_granule > vma_pagesize) { > + ret = kvm_mmu_topup_memory_cache(memcache, > + kvm_mmu_cache_min_pages(kvm)); > + if (ret) > + return ret; > + } As I explained in v1 [1], this looks correct to me. I still think that someone else should have a look, but if Marc decides to pick up this patch as-is, he can add my Reviewed-by: Alexandru Elisei . [1] https://lore.kernel.org/lkml/2c65bff2-be7f-b20c-9265-939bc73185b6@arm.com/ Thanks, Alex > + > /* > * Under the premise of getting a FSC_PERM fault, we just need to relax > * permissions only if vma_pagesize equals fault_granule. Otherwise,