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Wed, 19 Aug 2020 00:38:47 -0400 X-MC-Unique: Jz_5CkvTNPGgx4CrGc2ODg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1AE20186A561; Wed, 19 Aug 2020 04:38:46 +0000 (UTC) Received: from [10.64.54.198] (vpn2-54-198.bne.redhat.com [10.64.54.198]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 20EDA7849A; Wed, 19 Aug 2020 04:38:43 +0000 (UTC) Subject: Re: [PATCH v2 01/22] KVM: arm64: Don't free memcache pages in kvm_phys_addr_ioremap() To: Will Deacon , kvmarm@lists.cs.columbia.edu References: <20200818132818.16065-1-will@kernel.org> <20200818132818.16065-2-will@kernel.org> From: Gavin Shan Message-ID: <47f7bfc2-1880-908f-4345-b25da500b0ff@redhat.com> Date: Wed, 19 Aug 2020 14:38:39 +1000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: <20200818132818.16065-2-will@kernel.org> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=gshan@redhat.com X-Mimecast-Spam-Score: 0.002 X-Mimecast-Originator: redhat.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200819_003856_695961_CE9F995A X-CRM114-Status: GOOD ( 20.09 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Gavin Shan Cc: Marc Zyngier , kernel-team@android.com, linux-arm-kernel@lists.infradead.org, Catalin Marinas Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Will, On 8/18/20 11:27 PM, Will Deacon wrote: > kvm_phys_addr_ioremap() unconditionally empties out the memcache pages > for the current vCPU on return. This causes subsequent topups to allocate > fresh pages and is at odds with the behaviour when mapping memory in > user_mem_abort(). > > Remove the call to kvm_mmu_free_memory_cache() from > kvm_phys_addr_ioremap(), allowing the cached pages to be used by a later > mapping. > > Cc: Marc Zyngier > Cc: Quentin Perret > Signed-off-by: Will Deacon > --- > arch/arm64/kvm/mmu.c | 6 ++---- > 1 file changed, 2 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 662b0c99a63d..4a24ebdc6fc6 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1489,19 +1489,17 @@ int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa, > ret = kvm_mmu_topup_memory_cache(&cache, > kvm_mmu_cache_min_pages(kvm)); > if (ret) > - goto out; > + break; > spin_lock(&kvm->mmu_lock); > ret = stage2_set_pte(&kvm->arch.mmu, &cache, addr, &pte, > KVM_S2PTE_FLAG_IS_IOMAP); > spin_unlock(&kvm->mmu_lock); > if (ret) > - goto out; > + break; > > pfn++; > } > > -out: > - kvm_mmu_free_memory_cache(&cache); > return ret; > } > It seems incorrect. The cache is tracked by local variable (@cache), meaning the cache is only visible to kvm_phys_addr_ioremap() and its callee. So it's correct to free unused pages in two cases: (1) error is returned (2) high level of page tables were previously populated and not all pre-allocated pages are used. Otherwise, this leads to memory leakage. Thanks, Gavin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel