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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id DC71BC433F5 for ; Tue, 11 Jan 2022 10:22:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237717AbiAKKWx (ORCPT ); Tue, 11 Jan 2022 05:22:53 -0500 Received: from dfw.source.kernel.org ([139.178.84.217]:45160 "EHLO dfw.source.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233911AbiAKKWw (ORCPT ); Tue, 11 Jan 2022 05:22:52 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 68DC06156D for ; Tue, 11 Jan 2022 10:22:52 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id C2F22C36AF2; Tue, 11 Jan 2022 10:22:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1641896571; bh=HbZF3sztPtTkN6ALrGsuTJUFcv/QYl5hN7mRZyThhxk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=QsK4N6ZVg4xpfSCf+0LJtl3nX/2jJeeT1v36KyJ3jGmigu3P82wPjLAAm7CgvsmOB T1d/UxQbiJIN/nMCUusyQgva4iJURF3H5StcA5uLoabCMSU7LOZSTMjHmVcEbTwaKM H+jupVYLajPAhzCCfPynhwrP9ioUeEX8N0eXfCMXqUQ89GUzQrgV1RHrkVOUWeiXLD OJrCMdxWuvVyQY/AgpkE2RXDt/geRGaebeIzT2AwEoIpkG+pI9AZ3PVUUtXJ7AxHXr 5m7VLFto/oqk+W+UH6MBNTZTIwykOE77LuabiZNcm3S/9uiOE04dUWs4C2oCoDpzTi S76XymIe/ERGg== Received: from sofa.misterjones.org ([185.219.108.64] helo=why.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1n7EIj-00HM2A-83; Tue, 11 Jan 2022 10:22:49 +0000 Date: Tue, 11 Jan 2022 10:22:48 +0000 Message-ID: <87czkytvuv.wl-maz@kernel.org> From: Marc Zyngier To: Jing Zhang Cc: KVM , KVMARM , Will Deacon , Paolo Bonzini , David Matlack , Oliver Upton , Reiji Watanabe Subject: Re: [RFC PATCH 2/3] KVM: arm64: Add fast path to handle permission relaxation during dirty logging In-Reply-To: <20220110210441.2074798-3-jingzhangos@google.com> References: <20220110210441.2074798-1-jingzhangos@google.com> <20220110210441.2074798-3-jingzhangos@google.com> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/27.1 (x86_64-pc-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=US-ASCII X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: jingzhangos@google.com, kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu, will@kernel.org, pbonzini@redhat.com, dmatlack@google.com, oupton@google.com, reijiw@google.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, 10 Jan 2022 21:04:40 +0000, Jing Zhang wrote: > > To reduce MMU lock contention during dirty logging, all permission > relaxation operations would be performed under read lock. > > Signed-off-by: Jing Zhang > --- > arch/arm64/kvm/mmu.c | 50 ++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 50 insertions(+) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index cafd5813c949..dd1f43fba4b0 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -1063,6 +1063,54 @@ static int sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn, > return 0; > } > > +static bool fast_mark_writable(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > + struct kvm_memory_slot *memslot, unsigned long fault_status) > +{ > + int ret; > + bool writable; > + bool write_fault = kvm_is_write_fault(vcpu); > + gfn_t gfn = fault_ipa >> PAGE_SHIFT; > + kvm_pfn_t pfn; > + struct kvm *kvm = vcpu->kvm; > + bool logging_active = memslot_is_logging(memslot); > + unsigned long fault_level = kvm_vcpu_trap_get_fault_level(vcpu); > + unsigned long fault_granule; > + > + fault_granule = 1UL << ARM64_HW_PGTABLE_LEVEL_SHIFT(fault_level); > + > + /* Make sure the fault can be handled in the fast path. > + * Only handle write permission fault on non-hugepage during dirty > + * logging period. > + */ Not the correct comment format. > + if (fault_status != FSC_PERM || fault_granule != PAGE_SIZE > + || !logging_active || !write_fault) > + return false; This is all reinventing the logic that already exists in user_mem_abort(). I'm sympathetic to the effort not to bloat it even more, but code duplication doesn't help either. > + > + > + /* Pin the pfn to make sure it couldn't be freed and be resued for > + * another gfn. > + */ > + pfn = __gfn_to_pfn_memslot(memslot, gfn, true, NULL, > + write_fault, &writable, NULL); > + if (is_error_pfn(pfn) || !writable) > + return false; What happens if we hit a non-writable mapping? Don't we leak a page reference? > + > + read_lock(&kvm->mmu_lock); > + ret = kvm_pgtable_stage2_relax_perms( > + vcpu->arch.hw_mmu->pgt, fault_ipa, PAGE_HYP); PAGE_HYP? Err... no. KVM_PGTABLE_PROT_RW, more likely. Yes, they expand to the same thing, but you are not dealing with nVHE EL2 S1 page tables here. > + > + if (!ret) { > + kvm_set_pfn_dirty(pfn); > + mark_page_dirty_in_slot(kvm, memslot, gfn); > + } > + read_unlock(&kvm->mmu_lock); > + > + kvm_set_pfn_accessed(pfn); > + kvm_release_pfn_clean(pfn); > + > + return true; > +} > + > static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > struct kvm_memory_slot *memslot, unsigned long hva, > unsigned long fault_status) > @@ -1085,6 +1133,8 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa, > enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R; > struct kvm_pgtable *pgt; > > + if (fast_mark_writable(vcpu, fault_ipa, memslot, fault_status)) > + return 0; > fault_granule = 1UL << ARM64_HW_PGTABLE_LEVEL_SHIFT(fault_level); > write_fault = kvm_is_write_fault(vcpu); > exec_fault = kvm_vcpu_trap_is_exec_fault(vcpu); You are bypassing all sort of checks that I want to keep. Please integrate this in user_mem_abort instead of this side hack. Thanks, M. -- Without deviation from the norm, progress is not possible.