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 bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CC451CD8C92 for ; Mon, 8 Jun 2026 15:56:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc: To:From:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=2Q9Gr7IKyyrh6CkqHznMtILq2Yj9H3LSZNvYpyGmh8M=; b=x/wQvZaVE9yFLcfAK+voZzenxc 8ZpbE14yRSuqpfjjMum95ryi4BX+vUp3kcTDxsu1rNTIUO8z1q8OF4dbVVHn6obILqcopY6XB65Ut Za2YfSMdX3d9MMczfthDhgmCGgAMJgqb+Vh+CoPEI6dZ89EMypjO8B78TqiGSjUFN6dRB2d8js21M hheXAnVTjQQoLJ4fRfNvlFiacXq68Z4/PMwApSkBHdyfK3NrhxSGRxvMBaiJXPMHEoyJXwbxvnGfn lyc1w+r/EtFhpqWGRKlrerOrJCmNUzd6G1SbCrKBvzWRHTigQkcQ/t1aEYzK+F7PL6Ewq84NCYrhP PulcIf7Q==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wWcKP-000000040le-0zNL; Mon, 08 Jun 2026 15:55:53 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.99.1 #2 (Red Hat Linux)) id 1wWcKM-000000040lB-3jca for linux-arm-kernel@lists.infradead.org; Mon, 08 Jun 2026 15:55:52 +0000 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 D9CE7175A; Mon, 8 Jun 2026 08:55:44 -0700 (PDT) Received: from devkitleo.cambridge.arm.com (devkitleo.cambridge.arm.com [10.1.196.90]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5858B3FD80; Mon, 8 Jun 2026 08:55:47 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1780934149; bh=veGBV30tkSQy3O+cpkSjv7ZCdMRJYieHFctPW8nTs6c=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Y8CzEdVWkK52WP2X2Wny7eBG1Cf0NkljIogcHYA+LhhrKB6mOLLiYeTg5NFrn6raD nvII1zooStZ5FIIpNg8OZHUWrW2ALX1U0FlMgy5kdM/QXx9EwTCF5fWgJfHhXvFOPn S/WkUNKVm+eUnTONsxYe7wj4TQQoAoC3feJouD/E= From: Leonardo Bras To: Wei-Lin Chang Cc: Leonardo Bras , linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org, Marc Zyngier , Oliver Upton , Joey Gouly , Steffen Eiden , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Gavin Shan Subject: Re: [PATCH 1/2] KVM: arm64: Replace memslot_is_logging() with kvm_slot_dirty_track_enabled() Date: Mon, 8 Jun 2026 16:55:45 +0100 Message-ID: X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260605153248.2412064-2-weilin.chang@arm.com> References: <20260605153248.2412064-1-weilin.chang@arm.com> <20260605153248.2412064-2-weilin.chang@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260608_085551_021516_DE54EFAE X-CRM114-Status: GOOD ( 32.43 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Wei Lin, On Fri, Jun 05, 2026 at 04:32:47PM +0100, Wei-Lin Chang wrote: > When checking whether a memslot has dirty logging enabled, the > KVM_MEM_LOG_DIRTY_PAGES flag is the source of truth. Previously we were > using memslot_is_logging() which only tests dirty bitmap and did not > consider dirty ring. This was not detected because > KVM_CAP_DIRTY_LOG_RING_WITH_BITMAP was introduced together with KVM > arm64 dirty ring, and users need to enable it to ensure dirty > information is not lost for the case of VGIC LPI/ITS table changes. > > Fix this by using kvm_slot_dirty_track_enabled() instead which checks > KVM_MEM_LOG_DIRTY_PAGES. > > Note that memslot_is_logging() also treats a memslot as not logging if > KVM_MEM_READONLY is set, hence a memslot with both dirty logging and > read only would be seen as not logging for memslot_is_logging(), but > logging for kvm_slot_dirty_track_enabled(). This allows a read only > mapping of size > PAGE_SIZE to be built when memslot_is_logging() is > used, leading to a better read performance compared to > kvm_slot_dirty_track_enabled(). However memslots that have both > KVM_MEM_LOG_DIRTY_PAGES and KVM_MEM_READONLY set do not really make > sense as dirty logging is essentially nop for a read only memslot, so > this shouldn't affect real workloads much. It worries me a bit that we are ignoring the KVM_MEM_READONLY flag... I have not yet gone through the whole s2_mmu code but IIUC we can have scenarios on which a memslot can be read-only and have dirty-logging enabled. If a memslot is not faulted yet, IIUC it is marked as read-only (so it can be mapped on write fault), and we can have dirty-logging enabled for it as well (as the VMM has no idea). Would not that change impact this scenario? I will take a better look in that part of the code as well, to properly understand it. Thanks! Leo > > Fixes: 9cb1096f8590 ("KVM: arm64: Enable ring-based dirty memory tracking") > Signed-off-by: Wei-Lin Chang > --- > It took me a long investigation to acquire the context needed to > understand this change, however the reason for this problem not being > detected is an educated guess. Please let me know if this is wrong or > if there are other issues, thanks! > > arch/arm64/kvm/mmu.c | 11 +++-------- > 1 file changed, 3 insertions(+), 8 deletions(-) > > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c > index 4da9281312eb..06c46124d3e7 100644 > --- a/arch/arm64/kvm/mmu.c > +++ b/arch/arm64/kvm/mmu.c > @@ -161,11 +161,6 @@ static int kvm_mmu_split_huge_pages(struct kvm *kvm, phys_addr_t addr, > return ret; > } > > -static bool memslot_is_logging(struct kvm_memory_slot *memslot) > -{ > - return memslot->dirty_bitmap && !(memslot->flags & KVM_MEM_READONLY); > -} > - > /** > * kvm_arch_flush_remote_tlbs() - flush all VM TLB entries for v7/8 > * @kvm: pointer to kvm structure. > @@ -1748,7 +1743,7 @@ static short kvm_s2_resolve_vma_size(const struct kvm_s2_fault_desc *s2fd, > { > short vma_shift; > > - if (memslot_is_logging(s2fd->memslot)) { > + if (kvm_slot_dirty_track_enabled(s2fd->memslot)) { > s2vi->max_map_size = PAGE_SIZE; > vma_shift = PAGE_SHIFT; > } else { > @@ -1953,7 +1948,7 @@ static int kvm_s2_fault_compute_prot(const struct kvm_s2_fault_desc *s2fd, > *prot = KVM_PGTABLE_PROT_R; > > if (s2vi->map_writable && (s2vi->device || > - !memslot_is_logging(s2fd->memslot) || > + !kvm_slot_dirty_track_enabled(s2fd->memslot) || > kvm_is_write_fault(s2fd->vcpu))) > *prot |= KVM_PGTABLE_PROT_W; > > @@ -2084,7 +2079,7 @@ static int user_mem_abort(const struct kvm_s2_fault_desc *s2fd) > * and a write fault needs to collapse a block entry into a table. > */ > memcache = get_mmu_memcache(s2fd->vcpu); > - if (!perm_fault || (memslot_is_logging(s2fd->memslot) && > + if (!perm_fault || (kvm_slot_dirty_track_enabled(s2fd->memslot) && > kvm_is_write_fault(s2fd->vcpu))) { > ret = topup_mmu_memcache(s2fd->vcpu, memcache); > if (ret) > -- > 2.43.0 >