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Mon, 06 Jul 2026 14:46:04 -0700 (PDT) Date: Mon, 6 Jul 2026 14:46:03 -0700 In-Reply-To: Mime-Version: 1.0 References: <20260702142912.6395-1-alexandru.elisei@arm.com> <20260702142912.6395-2-alexandru.elisei@arm.com> <8a24f016-6f0f-4322-b646-d843f6fa481e@arm.com> Message-ID: Subject: Re: [RFC PATCH 1/3] KVM: guest_memfd: Use memslot id to keep track of associated memslots From: Sean Christopherson To: Alexandru Elisei Cc: David Hildenbrand , pbonzini@redhat.com, kvm@vger.kernel.org, maz@kernel.org, oupton@kernel.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, fuad.tabba@linux.dev, mark.rutland@arm.com Content-Type: text/plain; charset="us-ascii" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260706_144605_867603_FBE92458 X-CRM114-Status: GOOD ( 21.15 ) 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 On Mon, Jul 06, 2026, Alexandru Elisei wrote: > On Mon, Jul 06, 2026 at 09:14:59AM +0200, David Hildenbrand wrote: > > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > > > index db57c5766ab6..43ef8e908aaf 100644 > > > --- a/virt/kvm/guest_memfd.c > > > +++ b/virt/kvm/guest_memfd.c > > > @@ -25,6 +25,7 @@ struct gmem_file { > > > struct kvm *kvm; > > > struct xarray bindings; > > > struct list_head entry; > > > + bool found_memslot; /* Used for balancing invalidations when punching a hole */ > > > > Probabably best to document what it means, not only what it is used for (and > > maybe document above the member if you end up with more text). > > Sure, this is how I changed it: > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c > index 210bdd76f0aa..3cee64047bce 100644 > --- a/virt/kvm/guest_memfd.c > +++ b/virt/kvm/guest_memfd.c > @@ -25,7 +25,13 @@ struct gmem_file { > struct kvm *kvm; > struct xarray bindings; > struct list_head entry; > - bool found_memslot; /* Used for balancing invalidations when punching a hole */ > + /* > + * Keeps track of whether memory has been unmapped during secondary MMU > + * invalidation, to keep the invalidate start and end calls balanced. > + * > + * Accessed while holding the inode->i_mapping lock in exclusive mode. > + */ > + bool memslot_invalidated; > }; > > Hopefully the new name is better. Why add a boolean? It's not _needed_ to balance updates, or rather it shouldn't be needed. filemap_invalidate_lock() prevents modifying bindings while an invalidation is in-progress. It might be a performation optimization, but if so, it's a premature one and belongs in a separate patch.