linux-kernel - Re: [PATCH v2 06/19] drivers core: Add I/O ASID allocator

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <856b0457-bd2f-c2af-fdeb-45fe0bd3136b@arm.com>
Date:   Fri, 26 Apr 2019 12:47:43 +0100
From:   Jean-Philippe Brucker <jean-philippe.brucker@....com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Christoph Hellwig <hch@...radead.org>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Andriy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        David Woodhouse <dwmw2@...radead.org>,
        "christian.koenig@....com" <christian.koenig@....com>
Subject: Re: [PATCH v2 06/19] drivers core: Add I/O ASID allocator

On 25/04/2019 19:19, Jacob Pan wrote:
> Hi Christoph,
> 
> On Tue, 23 Apr 2019 23:19:03 -0700
> Christoph Hellwig <hch@...radead.org> wrote:
> 
>> On Tue, Apr 23, 2019 at 04:31:06PM -0700, Jacob Pan wrote:
>>> The allocator doesn't really belong in drivers/iommu because some
>>> drivers would like to allocate PASIDs for devices that aren't
>>> managed by an IOMMU, using the same ID space as IOMMU. It doesn't
>>> really belong in drivers/pci either since platform device also
>>> support PASID. Add the allocator in drivers/base.  
>>
>> I'd still add it to drivers/iommu, just selectable separately from the
>> core iommu code..
> Perhaps I misunderstood. If a driver wants to use IOASIDs w/o iommu
> subsystem even turned on, how could selecting from the core iommu code
> help? Could you elaborate on "selectable"?

How about doing the same as CONFIG_IOMMU_IOVA? The code is in
drivers/iommu but can be selected by non-IOMMU_API users, independently
of CONFIG_IOMMU_SUPPORT. It's true that this allocator will mostly be
used by IOMMU drivers.

> From VT-d's perspective, PASIDs are only used with IOMMU on. Jean
> knows other use cases.

I know of one: the AMD GPU driver may use IOASID for context IDs, even
if IOMMU is disabled. As I understand it, if IOMMU is enabled they need
to use the same allocator as IOMMU since it's the same ID space. And I
think it's more convenient to use the same allocation code in the GPU
driver regardless of CONFIG_IOMMU_SUPPORT.

See the previous discussion at
https://www.spinics.net/lists/iommu/msg31200.html

Thanks,
Jean