Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Mon, 22 May 2023 23:45:12 -0700
From:   Christoph Hellwig <hch@infradead.org>
To:     Alistair Popple <apopple@nvidia.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, robin.murphy@arm.com,
        will@kernel.org, nicolinc@nvidia.com,
        linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org,
        kvmarm@lists.cs.columbia.edu, jgg@nvidia.com,
        John Hubbard <jhubbard@nvidia.com>
Subject: Re: [PATCH] mmu_notifiers: Notify on pte permission upgrades
Message-ID: <ZGxg+I8FWz3YqBMk@infradead.org>
References: <20230522063725.284686-1-apopple@nvidia.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20230522063725.284686-1-apopple@nvidia.com>
Precedence: bulk

On Mon, May 22, 2023 at 04:37:25PM +1000, Alistair Popple wrote:
> This problem was discovered during testing of an ARM SMMU
> implementation that does not support broadcast TLB maintenance
> (BTM). In this case the SMMU driver uses notifiers to issue TLB
> invalidates. For read-only to read-write pte upgrades the SMMU
> continually returned a read-only PTE to the device, even though the
> CPU had a read-write PTE installed.
> 
> Sending a mmu notifier event to the SMMU driver fixes the problem by
> flushing secondary TLB entries. A new notifier event type is added so
> drivers may filter out these invalidations if not required. Note a
> driver should never upgrade or install a PTE in response to this mmu
> notifier event as it is not synchronised against other PTE operations.

I don't see these SMMU driver changes anywhere.  I.e. you're adding dead
code as far as I can tell.