linux-kernel - Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID allocation and free it on mm exit

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Message-ID: <22b659c7-e972-7a56-2bd7-8df3b4820d4e@intel.com>
Date:   Mon, 25 Apr 2022 08:55:46 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
Cc:     "zhangfei.gao@...mail.com" <zhangfei.gao@...mail.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Joerg Roedel <joro@...tes.org>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        x86 <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, will@...nel.org,
        robin.murphy@....com, zhangfei.gao@...aro.org
Subject: Re: [PATCH v4 05/11] iommu/sva: Assign a PASID to mm on PASID
 allocation and free it on mm exit

On 4/25/22 07:26, Jean-Philippe Brucker wrote:
>>
>> How does the IOMMU hardware know that all activity to a given PASID is
>> finished?  That activity should, today, be independent of an mm or a
>> fd's lifetime.
> In the case of uacce, it's tied to the fd lifetime: opening an accelerator
> queue calls iommu_sva_bind_device(), which sets up the PASID context in
> the IOMMU. Closing the queue calls iommu_sva_unbind_device() which
> destroys the PASID context (after the device driver stopped all DMA for
> this PASID).

Could this PASID context destruction move from being "fd-based" to
happening under mm_pasid_drop()?  Logically, it seems like that should
work because mm_pasid_drop() happens after exit_mmap() where the VMAs
(which hold references to 'struct file' via vma->vm_file) are torn down.