Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:18 as permitted sender) client-ip=2620:137:e000::1:18;
Message-ID: <8c044e49-74bb-df56-8a60-663013c0910e@intel.com>
Date:   Tue, 26 Apr 2022 08:27:00 -0700
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.7.0
Subject: Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID
 allocation and free it on mm exit
Content-Language: en-US
To:     Jean-Philippe Brucker <jean-philippe@linaro.org>
Cc:     "zhangfei.gao@foxmail.com" <zhangfei.gao@foxmail.com>,
        Fenghua Yu <fenghua.yu@intel.com>,
        Joerg Roedel <joro@8bytes.org>,
        Ravi V Shankar <ravi.v.shankar@intel.com>,
        Tony Luck <tony.luck@intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        x86 <x86@kernel.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        iommu <iommu@lists.linux-foundation.org>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        Thomas Gleixner <tglx@linutronix.de>, will@kernel.org,
        robin.murphy@arm.com, zhangfei.gao@linaro.org
References: <tencent_76E043C4D1B6A21A5253579A61034107EB06@qq.com>
 <tencent_7477100F8A445C6CAFA8F13601A55134480A@qq.com>
 <YmJ/WA6KAQU/xJjA@myrica>
 <tencent_A4E83BA6071B2204B6F5D4E69A50D21C1A09@qq.com>
 <YmLOznyBF0f7COYT@myrica>
 <tencent_2922DAB6F3D5789A1CD3A21A843B4007ED09@qq.com>
 <Yman5hLomw9/c+bi@myrica> <76ec6342-0d7c-7c7b-c132-2892e4048fa1@intel.com>
 <YmavoKkVu+hd+x0M@myrica> <22b659c7-e972-7a56-2bd7-8df3b4820d4e@intel.com>
 <YmbO/l5IwfBCHrl8@myrica>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <YmbO/l5IwfBCHrl8@myrica>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 4/25/22 09:40, Jean-Philippe Brucker wrote:
> The problem is that we'd have to request the device driver to stop DMA
> before we can destroy the context and free the PASID. We did consider
> doing this in the release() MMU notifier, but there were concerns about
> blocking mmput() for too long (for example
> https://lore.kernel.org/linux-iommu/4d68da96-0ad5-b412-5987-2f7a6aa796c3@amd.com/
> though I think there was a more recent discussion). We also need to drain
> the PRI and fault queues to get rid of all references to that PASID.

Is the concern truly about blocking mmput() itself?  Or, is it about
releasing the resources associated with the mm?