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From: Christoph Hellwig <hch@infradead.org>
To: "Christian König" <christian.koenig@amd.com>
Cc: Jean-Philippe Brucker <jean-philippe@linaro.org>,
	kevin.tian@intel.com, devicetree@vger.kernel.org, jgg@ziepe.ca,
	linux-pci@vger.kernel.org, robin.murphy@arm.com,
	linux-mm@kvack.org, iommu@lists.linux-foundation.org,
	catalin.marinas@arm.com, zhangfei.gao@linaro.org,
	will@kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v5 02/25] iommu/sva: Manage process address spaces
Date: Mon, 20 Apr 2020 04:55:04 -0700
Message-ID: <20200420115504.GA20664@infradead.org> (raw)
In-Reply-To: <6b195512-fa73-9a49-03d8-1ed92e86f607@amd.com>

On Mon, Apr 20, 2020 at 01:44:56PM +0200, Christian König wrote:
> Am 20.04.20 um 10:10 schrieb Christoph Hellwig:
> > On Mon, Apr 20, 2020 at 09:42:13AM +0200, Jean-Philippe Brucker wrote:
> > > Right, I can see the appeal. I still like having a single mmu notifier per
> > > mm because it ensures we allocate a single PASID per mm (as required by
> > > x86). I suppose one alternative is to maintain a hashtable of mm->pasid,
> > > to avoid iterating over all bonds during allocation.
> > Given that the PASID is a pretty generic and important concept can
> > we just add it directly to the mm_struct and allocate it lazily once
> > we first need it?
> 
> Well the problem is that the PASID might as well be device specific. E.g.
> some devices use 16bit PASIDs, some 15bit, some other only 12bit.
> 
> So what could (at least in theory) happen is that you need to allocate
> different PASIDs for the same process because different devices need one.

This directly contradicts the statement from Jean-Philippe above that
x86 requires a single PASID per mm_struct.  If we may need different
PASIDs for different devices and can actually support this just
allocating one per [device, mm_struct] would make most sense of me, as
it doesn't couple otherwise disjoint state.
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Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-14 17:02 [PATCH v5 00/25] iommu: Shared Virtual Addressing and SMMUv3 support Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 01/25] mm/mmu_notifiers: pass private data down to alloc_notifier() Jean-Philippe Brucker
2020-04-14 18:09   ` Jason Gunthorpe
2020-04-14 17:02 ` [PATCH v5 02/25] iommu/sva: Manage process address spaces Jean-Philippe Brucker
2020-04-16  7:28   ` Christoph Hellwig
2020-04-16  8:54     ` Jean-Philippe Brucker
2020-04-16 12:13       ` Christoph Hellwig
2020-04-20  7:42         ` Jean-Philippe Brucker
2020-04-20  8:10           ` Christoph Hellwig
2020-04-20 11:44             ` Christian König
2020-04-20 11:55               ` Christoph Hellwig [this message]
2020-04-20 12:40                 ` Christian König
2020-04-20 15:00                   ` Felix Kuehling
2020-04-20 17:44                     ` Jacob Pan
2020-04-20 17:52                       ` Felix Kuehling
2020-04-20 13:57           ` Jason Gunthorpe
2020-04-20 17:48             ` Jacob Pan
2020-04-20 18:14               ` Fenghua Yu
2020-04-21  8:55                 ` Christoph Hellwig
2020-04-14 17:02 ` [PATCH v5 03/25] iommu: Add a page fault handler Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 04/25] iommu/sva: Search mm by PASID Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 05/25] iommu/iopf: Handle mm faults Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 06/25] iommu/sva: Register page fault handler Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 07/25] arm64: mm: Add asid_gen_match() helper Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 08/25] arm64: mm: Pin down ASIDs for sharing mm with devices Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 09/25] iommu/io-pgtable-arm: Move some definitions to a header Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 10/25] iommu/arm-smmu-v3: Manage ASIDs with xarray Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 11/25] arm64: cpufeature: Export symbol read_sanitised_ftr_reg() Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 12/25] iommu/arm-smmu-v3: Share process page tables Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 13/25] iommu/arm-smmu-v3: Seize private ASID Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 14/25] iommu/arm-smmu-v3: Add support for VHE Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 15/25] iommu/arm-smmu-v3: Enable broadcast TLB maintenance Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 16/25] iommu/arm-smmu-v3: Add SVA feature checking Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 17/25] iommu/arm-smmu-v3: Implement mm operations Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 18/25] iommu/arm-smmu-v3: Hook up ATC invalidation to mm ops Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 19/25] iommu/arm-smmu-v3: Add support for Hardware Translation Table Update Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 20/25] iommu/arm-smmu-v3: Maintain a SID->device structure Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 21/25] dt-bindings: document stall property for IOMMU masters Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 22/25] iommu/arm-smmu-v3: Add stall support for platform devices Jean-Philippe Brucker
2020-04-14 17:02 ` [PATCH v5 23/25] PCI/ATS: Add PRI stubs Jean-Philippe Brucker
2020-04-14 18:03   ` Kuppuswamy, Sathyanarayanan
2020-04-14 17:02 ` [PATCH v5 24/25] PCI/ATS: Export PRI functions Jean-Philippe Brucker
2020-04-14 18:03   ` Kuppuswamy, Sathyanarayanan
2020-04-14 17:02 ` [PATCH v5 25/25] iommu/arm-smmu-v3: Add support for PRI Jean-Philippe Brucker

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