From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793905463; b=ODEYABxGsEIkXi6T6tTBVypYw2ix7UVYDUKjUvF8XeW95rkZ30wv3Ka3muw83W+nwlZP uW4mMA0pScMYpJbnIH53RldF2NWIOamfPJdHiMAfeel0KQcn9ioTLoBgo/JvnoLTzsIYE JSYTWWK57S4V27WMCzKXUEQcx9SABVjMMyY++BPKHGmVMHmX7wDnbMRjAZ+61Gr/RdWFH Bt46LENiiSRhDdV/VHFmaipF6GZwJDULtbqL6ilMAY92NWGum/DUsAs8jLRZDkkJTWJja Ecy33QvrATXl70wnncM4WLUPuF4Uvhe46YKjEImavcrntcUf42GdPOdqaEHwDQQ5ACg== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793905463; h=Received:DKIM-Signature:Date:From:To:Cc:Subject:Message-ID: References:MIME-Version:Content-Type:Content-Disposition:In-Reply-To; bh=rLWhvCj1UCjx0H2m7OWzapN/VPTtDSdiXxZNIfUhXCM=; b=agUXsLxaDLKE1gxfMdsp1xUB/xsfzbuVKVuLDqD4PGGxq4kBcCQ4KPgz58JR1tldoTml h4APP8HnQ81lNr258iZy1/zu74RBHTgWwqjjFhfCsgiOZ5MqHpDtutYbYYsBaKB8x41nK jLHjxAT1QYuuKICDxWLg19DWQi5ZIRwNOa4fB8PGUUmzrpNjIRlcQ2tS+hqm0Vs0hTbw2 ZRTKNGB1tb23iAwqeQK4k75pQPv7Vtk086so24h8pGtNqhfG5ZY6tfT/1wVb+PH+bnCaP bX0TaiNvM1TjDyLLWn8UtAPsOkKYYMklu/+uINe76TWsPkBwa2ObpOiryOv8c5vvk7A== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=a7KRn5UW; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 7DC15606A326; Thu, 5 Nov 2026 19:04:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=a7KRn5UW Received: by smtp.kernel.org (Postfix) with ESMTPSA id AAFCB1F000C1; Thu, 5 Nov 2026 19:04:20 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793905463; bh=rLWhvCj1UCjx0H2m7OWzapN/VPTtDSdiXxZNIfUhXCM=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=a7KRn5UWkD2bg4mfjBaHuZrPBFOQU5noiWBtxbTkRkapYFkzbJooltue1tjMDltFe nQlN1aMdJhscG3nBcJHrK/xth/cma7LTfimTmBAi6sSO48Dwcx52pdvqIfLeFY983J rKElw5cUOWFv+QQns+wpIZnzGGakfW2UyQMgI1DSLqq7FTSlMGkk0PPwe96V9vmfWd dFEDVFmxdKSJhJxngaUkdu0iL1/dwXyr8bsBJWmdzJyZ/bN7VBZY5y71k+/PB1a7cr MCRttZFECSUq18Votb38NZ571RtsP+oIP1IubyMUXpYn4NLj/mxCpIc8KyHAG2aUcW qEsxvANNTEo5w== Date: Thu, 5 Nov 2026 19:04:18 +0000 From: "Lorenzo Stoakes (ARM)" To: Sean Christopherson Cc: Alexandru Elisei , pbonzini@redhat.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, maz@kernel.org, oupton@kernel.org, suzuki.poulose@arm.com, kvmarm@lists.linux.dev, linux-arm-kernel@lists.infradead.org, david@kernel.org, mark.rutland@arm.com, ackerleytng@google.com Subject: Re: [PATCH v2] KVM: Ignore MMU notifiers for guest_memfd-only memslots Message-ID: References: <20260714160411.302386-1-alexandru.elisei@arm.com> X-Mailing-List: kvm@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Nov 05, 2026 at 11:02:28AM -0800, Sean Christopherson wrote: > On Wed, Nov 04, 2026, Lorenzo Stoakes (ARM) wrote: > > [updated David's email address to @kernel.org] > > > > On Wed, Aug 12, 2026 at 10:42:50AM +0100, Alexandru Elisei wrote: > > [ ... ] > > > On Fri, Jul 24, 2026 at 12:52:20PM -0700, Sean Christopherson wrote: > > > > It'll probably take me a few weeks to circle back to this, as I finally crawled > > > > out from underneath a pile of urgent and am just now getting back into review > > > > mode, but this is fairly high on my todo list, so with luck we might still squeeze > > > > this into 7.3. > > > > Hey Sean, > > > > I wondered whether you'd had a chance to look at this? > > > > After discussing this with Marc and Alex it is clear that this is really a > > blocker for Alex's SPE series, as we need a sensible means of ensuring > > that stage-2 mappings stay in place. > > > > So ideally would prefer to get something like this in in the next cycle, > > if you don't have any objections to it? :) > > > > If it'd be easier, I think a smaller version of the same patch would also > > give us what we need? I.e. your snippet from June with the page ageing part > > dropped, as below. > > The GPC invalidation fix landed, so we can go straight to the super simple v1. > Compile tested only at this point, I'll formally post this (hopefully today), > assuming nothing explodes in testing. Perfect, thanks very much :) > > -- > From: Alexandru Elisei > Date: Mon, 15 Jun 2026 16:52:44 +0100 > Subject: [PATCH] KVM: Skip gfn-based MMU notifier invalidations for > guest_memfd-only memslots > > Don't invalidate gmem-only memslots when responding to MMU notifier > invalidations, as the entire point of gmem-only memslots is so that KVM > doesn't need a VMA to install mappings into KVM's MMU. Specificially, > page faults are resolved by going straight to guest_memfd, using the gfn > and the associated memslot's gmem.file. I.e. whether or not userspace > happens to have valid mappings to the same gmem instance is irrelevant, > as are any invalidations for those mappings. > > Note! The exception is KVM's gfn_to_pfn_cache implementation which isn't > yet wired up to pull pfns directly from guest_memfd, i.e. still relies on > userspace mappings/VMAs and thus need to be invalidated, e.g. to ensure KVM > doesn't retain a kernel mapping+pointer to PRIVATE memory. However, as of > commit da260bcb56fe ("KVM: pfncache: use a dedicated invalidation sequence > for cache refresh"), GPC invalidation no longer relies on memslot lookups, > because GPCs also support HVA-based mappings. I.e. KVM *must* be able to > detect and handle relevant MMU notifier invalidations even if there is *no* > memslot whatsoever. > > In addition to the obvious performance benefits, avoiding unnecessary and > spurious SPTE zaps and TLB flushes will allow KVM to support features like > ARM's Statistical Profiling Extension (SPE)[1] and x86's Secure AVIC[2], > both of which rely on the pages *never* being unmapped from the stage-2 > page tables. > > Link: https://lore.kernel.org/all/20260903160623.315525-1-alexandru.elisei@arm.com [1] > Link: https://lore.kernel.org/all/cover.1783490022.git.naveen@kernel.org [2] > Cc: Lorenzo Stoakes (ARM) > Cc: Naveen N Rao (AMD) > Signed-off-by: Alexandru Elisei > [sean: rewrite changelog to capture the new gpc behavior] > Signed-off-by: Sean Christopherson > --- > virt/kvm/kvm_main.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index cf4cb586f140..599dea22afb8 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -601,6 +601,10 @@ static __always_inline kvm_mn_ret_t kvm_handle_hva_range(struct kvm *kvm, > unsigned long hva_start, hva_end; > > slot = container_of(node, struct kvm_memory_slot, hva_node[slots->node_idx]); > + > + if (kvm_slot_has_gmem(slot) && kvm_memslot_is_gmem_only(slot)) > + continue; > + > hva_start = max_t(unsigned long, range->start, slot->userspace_addr); > hva_end = min_t(unsigned long, range->end, > slot->userspace_addr + (slot->npages << PAGE_SHIFT)); > > base-commit: d21eef2084a9af87ac2a783bc7c2b175ba114e4e > -- -- Cheers, Lorenzo