From: Robin Murphy <robin.murphy@arm.com>
To: Christoph Hellwig <hch@lst.de>
Cc: Joerg Roedel <joro@8bytes.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
Tom Lendacky <thomas.lendacky@amd.com>,
iommu@lists.linux-foundation.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 03/19] dma-iommu: don't use a scatterlist in iommu_dma_alloc
Date: Wed, 6 Feb 2019 15:28:28 +0000 [thread overview]
Message-ID: <f59852aa-394c-3165-f7c0-fa6cdcea059f@arm.com> (raw)
In-Reply-To: <20190201161638.GJ6532@lst.de>
On 01/02/2019 16:16, Christoph Hellwig wrote:
> On Fri, Feb 01, 2019 at 03:24:45PM +0000, Robin Murphy wrote:
>> On 14/01/2019 09:41, Christoph Hellwig wrote:
>>> Directly iterating over the pages makes the code a bit simpler and
>>> prepares for the following changes.
>>
>> It also defeats the whole purpose of __iommu_dma_alloc_pages(), so I'm not
>> really buying the simplification angle - you've *seen* that code, right? ;)
>
> How does it defeat the purpose of __iommu_dma_alloc_pages?
Because if iommu_map() only gets called at PAGE_SIZE granularity, then
the IOMMU PTEs will be created at PAGE_SIZE (or smaller) granularity, so
any effort to get higher-order allocations matching larger IOMMU block
sizes is wasted, and we may as well have just done this:
for (i = 0; i < count; i++) {
struct page *page = alloc_page(gfp);
...
iommu_map(..., page_to_phys(page), PAGE_SIZE, ...);
}
Really, it's a shame we have to split huge pages for the CPU remap,
since in the common case the CPU MMU will have a matching block size,
but IIRC there was something in vmap() or thereabouts that explicitly
chokes on them.
Robin.
next prev parent reply other threads:[~2019-02-06 15:28 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-14 9:41 implement generic dma_map_ops for IOMMUs Christoph Hellwig
2019-01-14 9:41 ` [PATCH 01/19] dma-mapping: add a Kconfig symbol to indicated arch_dma_prep_coherent presence Christoph Hellwig
2019-02-01 14:22 ` Robin Murphy
2019-02-01 16:12 ` Christoph Hellwig
2019-01-14 9:41 ` [PATCH 02/19] dma-iommu: cleanup dma-iommu.h Christoph Hellwig
2019-02-01 14:47 ` Robin Murphy
2019-02-01 16:13 ` Christoph Hellwig
2019-02-06 15:08 ` Robin Murphy
2019-02-11 15:59 ` Christoph Hellwig
2019-01-14 9:41 ` [PATCH 03/19] dma-iommu: don't use a scatterlist in iommu_dma_alloc Christoph Hellwig
2019-02-01 15:24 ` Robin Murphy
2019-02-01 16:16 ` Christoph Hellwig
2019-02-06 15:28 ` Robin Murphy [this message]
2019-02-11 16:00 ` Christoph Hellwig
2019-01-14 9:41 ` [PATCH 04/19] dma-iommu: remove the flush_page callback Christoph Hellwig
2019-02-01 15:28 ` Robin Murphy
2019-01-14 9:41 ` [PATCH 05/19] dma-iommu: move the arm64 wrappers to common code Christoph Hellwig
2019-01-14 9:41 ` [PATCH 06/19] dma-iommu: fix and refactor iommu_dma_mmap Christoph Hellwig
2019-02-05 15:02 ` Robin Murphy
2019-02-11 16:03 ` Christoph Hellwig
2019-01-14 9:41 ` [PATCH 07/19] dma-iommu: fix and refactor iommu_dma_get_sgtable Christoph Hellwig
2019-01-14 9:41 ` [PATCH 08/19] dma-iommu: move __iommu_dma_map Christoph Hellwig
2019-01-14 9:41 ` [PATCH 09/19] dma-iommu: refactor page array remap helpers Christoph Hellwig
2019-01-14 9:41 ` [PATCH 10/19] dma-iommu: factor atomic pool allocations into helpers Christoph Hellwig
2019-01-14 9:41 ` [PATCH 11/19] dma-iommu: factor contiguous " Christoph Hellwig
2019-01-14 9:41 ` [PATCH 12/19] dma-iommu: refactor iommu_dma_free Christoph Hellwig
2019-01-14 9:41 ` [PATCH 13/19] dma-iommu: don't remap contiguous allocations for coherent devices Christoph Hellwig
2019-01-14 9:41 ` [PATCH 14/19] dma-iommu: factor contiguous remapped allocations into helpers Christoph Hellwig
2019-01-14 9:41 ` [PATCH 15/19] dma-iommu: refactor iommu_dma_alloc Christoph Hellwig
2019-01-14 9:41 ` [PATCH 16/19] dma-iommu: don't depend on CONFIG_DMA_DIRECT_REMAP Christoph Hellwig
2019-02-06 11:55 ` Robin Murphy
2019-02-11 16:39 ` Christoph Hellwig
2019-01-14 9:41 ` [PATCH 17/19] dma-iommu: switch copyright boilerplace to SPDX Christoph Hellwig
2019-02-06 11:57 ` Robin Murphy
2019-01-14 9:41 ` [PATCH 18/19] arm64: switch copyright boilerplace to SPDX in dma-mapping.c Christoph Hellwig
2019-02-06 12:19 ` Robin Murphy
2019-01-14 9:41 ` [PATCH 19/19] arm64: trim includes " Christoph Hellwig
2019-01-28 7:53 ` implement generic dma_map_ops for IOMMUs Christoph Hellwig
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