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From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Arnd Bergmann <arnd@arndb.de>, Christoph Hellwig <hch@lst.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Ard Biesheuvel <ardb@kernel.org>,
	Isaac Manjarres <isaacmanjarres@google.com>,
	Saravana Kannan <saravanak@google.com>,
	Alasdair Kergon <agk@redhat.com>, Daniel Vetter <daniel@ffwll.ch>,
	Joerg Roedel <joro@8bytes.org>, Mark Brown <broonie@kernel.org>,
	Mike Snitzer <snitzer@kernel.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	linux-mm@kvack.org, iommu@lists.linux.dev,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 13/13] dma: arm64: Add CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC and enable it for arm64
Date: Mon, 7 Nov 2022 15:38:49 +0100	[thread overview]
Message-ID: <20221107143849.GA27946@lst.de> (raw)
In-Reply-To: <6e846f75-b330-9523-4356-41d5f9e48f12@arm.com>

On Mon, Nov 07, 2022 at 01:03:31PM +0000, Robin Murphy wrote:
> On 2022-11-06 22:01, Catalin Marinas wrote:
>> With all the infrastructure in place for bouncing small kmalloc()
>> buffers, add the corresponding Kconfig entry and select it for arm64.
>
> AFAICS we're missing the crucial part to ensure that SWIOTLB is available 
> even when max_pfn <= arm64_dma_phys_limit, which is very likely to be true 
> on low-memory systems that care most about kmalloc wastage. The only way to 
> override that currently is with "swiotlb=force", but bouncing *everything* 
> is not desirable either.

FYI, one of the reasons for the swiotlb_init refactor that passes
flags and a boolean a while ago is that we can trivially just either
pass another flag or check a condition in swiotlb_init to allocate the
buffer.  There's actually another case for which we need the
unconditional allocation, and that is the bouncing for untrusted
external devices with dma-iommu.

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@lst.de>
To: Robin Murphy <robin.murphy@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Arnd Bergmann <arnd@arndb.de>, Christoph Hellwig <hch@lst.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Herbert Xu <herbert@gondor.apana.org.au>,
	Ard Biesheuvel <ardb@kernel.org>,
	Isaac Manjarres <isaacmanjarres@google.com>,
	Saravana Kannan <saravanak@google.com>,
	Alasdair Kergon <agk@redhat.com>, Daniel Vetter <daniel@ffwll.ch>,
	Joerg Roedel <joro@8bytes.org>, Mark Brown <broonie@kernel.org>,
	Mike Snitzer <snitzer@kernel.org>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	linux-mm@kvack.org, iommu@lists.linux.dev,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v3 13/13] dma: arm64: Add CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC and enable it for arm64
Date: Mon, 7 Nov 2022 15:38:49 +0100	[thread overview]
Message-ID: <20221107143849.GA27946@lst.de> (raw)
In-Reply-To: <6e846f75-b330-9523-4356-41d5f9e48f12@arm.com>

On Mon, Nov 07, 2022 at 01:03:31PM +0000, Robin Murphy wrote:
> On 2022-11-06 22:01, Catalin Marinas wrote:
>> With all the infrastructure in place for bouncing small kmalloc()
>> buffers, add the corresponding Kconfig entry and select it for arm64.
>
> AFAICS we're missing the crucial part to ensure that SWIOTLB is available 
> even when max_pfn <= arm64_dma_phys_limit, which is very likely to be true 
> on low-memory systems that care most about kmalloc wastage. The only way to 
> override that currently is with "swiotlb=force", but bouncing *everything* 
> is not desirable either.

FYI, one of the reasons for the swiotlb_init refactor that passes
flags and a boolean a while ago is that we can trivially just either
pass another flag or check a condition in swiotlb_init to allocate the
buffer.  There's actually another case for which we need the
unconditional allocation, and that is the bouncing for untrusted
external devices with dma-iommu.

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linux-arm-kernel@lists.infradead.org
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  reply	other threads:[~2022-11-07 14:38 UTC|newest]

Thread overview: 90+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-06 22:01 [PATCH v3 00/13] mm, dma, arm64: Reduce ARCH_KMALLOC_MINALIGN to 8 Catalin Marinas
2022-11-06 22:01 ` Catalin Marinas
2022-11-06 22:01 ` [PATCH v3 01/13] mm/slab: Decouple ARCH_KMALLOC_MINALIGN from ARCH_DMA_MINALIGN Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-06 22:01 ` [PATCH v3 02/13] dma-mapping: Force bouncing if the kmalloc() size is not cacheline-aligned Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-07  9:43   ` Christoph Hellwig
2022-11-07  9:43     ` Christoph Hellwig
2022-11-06 22:01 ` [PATCH v3 03/13] iommu/dma: Force bouncing of the " Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-07  9:46   ` Christoph Hellwig
2022-11-07  9:46     ` Christoph Hellwig
2022-11-07 10:54     ` Catalin Marinas
2022-11-07 10:54       ` Catalin Marinas
2022-11-07 13:26       ` Robin Murphy
2022-11-07 13:26         ` Robin Murphy
2022-11-08 10:51         ` Catalin Marinas
2022-11-08 10:51           ` Catalin Marinas
2022-11-08 11:40           ` Robin Murphy
2022-11-08 11:40             ` Robin Murphy
2022-11-08  7:50       ` Christoph Hellwig
2022-11-08  7:50         ` Christoph Hellwig
2022-11-14 23:23   ` Isaac Manjarres
2022-11-14 23:23     ` Isaac Manjarres
2022-11-15 11:48     ` Catalin Marinas
2022-11-15 11:48       ` Catalin Marinas
2022-11-06 22:01 ` [PATCH v3 04/13] mm/slab: Allow kmalloc() minimum alignment fallback to dma_get_cache_alignment() Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-07  0:50   ` kernel test robot
2022-11-07  9:22     ` Catalin Marinas
2022-11-07  9:22       ` Catalin Marinas
2022-11-07  1:51   ` kernel test robot
2022-11-06 22:01 ` [PATCH v3 05/13] mm/slab: Simplify create_kmalloc_cache() args and make it static Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-06 22:01 ` [PATCH v3 06/13] dma: Allow the smaller cache_line_size() returned by dma_get_cache_alignment() Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-06 22:01 ` [PATCH v3 07/13] drivers/base: Use ARCH_DMA_MINALIGN instead of ARCH_KMALLOC_MINALIGN Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-06 22:01 ` [PATCH v3 08/13] drivers/gpu: " Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-06 22:01 ` [PATCH v3 09/13] drivers/usb: " Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-06 22:01 ` [PATCH v3 10/13] drivers/spi: " Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-07 12:58   ` Mark Brown
2022-11-07 12:58     ` Mark Brown
2022-11-06 22:01 ` [PATCH v3 11/13] crypto: " Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-07  2:22   ` Herbert Xu
2022-11-07  2:22     ` Herbert Xu
2022-11-07  9:05     ` Catalin Marinas
2022-11-07  9:05       ` Catalin Marinas
2022-11-07  9:12       ` Herbert Xu
2022-11-07  9:12         ` Herbert Xu
2022-11-07  9:38         ` Catalin Marinas
2022-11-07  9:38           ` Catalin Marinas
2022-11-06 22:01 ` [PATCH v3 12/13] drivers/md: " Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-06 22:01 ` [PATCH v3 13/13] dma: arm64: Add CONFIG_DMA_BOUNCE_UNALIGNED_KMALLOC and enable it for arm64 Catalin Marinas
2022-11-06 22:01   ` Catalin Marinas
2022-11-07 13:03   ` Robin Murphy
2022-11-07 13:03     ` Robin Murphy
2022-11-07 14:38     ` Christoph Hellwig [this message]
2022-11-07 14:38       ` Christoph Hellwig
2022-11-07 15:24       ` Robin Murphy
2022-11-07 15:24         ` Robin Murphy
2022-11-08  9:52     ` Catalin Marinas
2022-11-08  9:52       ` Catalin Marinas
2022-11-08 10:03       ` Christoph Hellwig
2022-11-08 10:03         ` Christoph Hellwig
2022-11-30 18:48         ` Isaac Manjarres
2022-11-30 18:48           ` Isaac Manjarres
2022-11-30 23:32           ` Alexander Graf
2022-11-30 23:32             ` Alexander Graf
2023-04-20 11:51             ` Petr Tesařík
2023-04-20 11:51               ` Petr Tesařík
2023-03-16 18:38 ` [PATCH v3 00/13] mm, dma, arm64: Reduce ARCH_KMALLOC_MINALIGN to 8 Isaac Manjarres
2023-03-16 18:38   ` Isaac Manjarres
2023-04-19 16:06   ` Catalin Marinas
2023-04-19 16:06     ` Catalin Marinas
2023-04-20  9:52     ` Petr Tesarik
2023-04-20  9:52       ` Petr Tesarik
2023-04-20 17:43       ` Catalin Marinas
2023-04-20 17:43         ` Catalin Marinas
2023-05-15 19:09     ` Isaac Manjarres
2023-05-15 19:09       ` Isaac Manjarres
2023-05-16 17:19       ` Catalin Marinas
2023-05-16 17:19         ` Catalin Marinas
2023-05-16 18:19         ` Isaac Manjarres
2023-05-16 18:19           ` Isaac Manjarres

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