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From: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
To: "Koenig, Christian" <Christian.Koenig-5C7GfCeVMHo@public.gmane.org>
Cc: Kate Stewart
	<kstewart-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>,
	Masayoshi Mizuma
	<m.mizuma-+CUm20s59erQFUHtdCDX3A@public.gmane.org>,
	"Maciej W. Rozycki"
	<macro-6z/3iImG2C8G8FEW9MqTrA@public.gmane.org>,
	Eric Biggers <ebiggers-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	Catalin Marinas <catalin.marinas-5wv7dgnIgG8@public.gmane.org>,
	Imre Deak <imre.deak-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
	dri-devel
	<dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org>,
	Chris Wilson
	<chris-Y6uKTt2uX1cEflXRtASbqLVCufUGDwFn@public.gmane.org>,
	Masahiro Yamada
	<yamada.masahiro-uWyLwvC0a2jby3iVrkZq2A@public.gmane.org>,
	Benjamin Gaignard
	<benjamin.gaignard-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>,
	Mauro Carvalho Chehab
	<mchehab+samsung-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Will Deacon <will-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>,
	Emil Velikov
	<emil.velikov-ZGY8ohtN/8qB+jHODAdFcQ@public.gmane.org>,
	Rob Clark <robdclark-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>,
	Michael Ellerman <mpe-Gsx/Oe8HsFggBc27wqDAHg@public.gmane.org>,
	Paul Burton <paul.burton-8NJIiSa5LzA@public.gmane.org>,
	Mike Rapoport <rppt-tEXmvtCZX7AybS5Ee8rs3A@public.gmane.org>,
	Geert Uytterhoeven
	<geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org>,
	"moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)"
	<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>,
	Daniel
Subject: Re: [PATCH 0/6] drm+dma: cache support for arm, etc
Date: Thu, 15 Aug 2019 20:27:42 +0200	[thread overview]
Message-ID: <20190815182742.GA20859@lst.de> (raw)
In-Reply-To: <e3f73b3c-49d5-3c19-dfff-0a24b4617e50-5C7GfCeVMHo@public.gmane.org>

On Thu, Aug 15, 2019 at 06:21:00PM +0000, Koenig, Christian wrote:
> >   (2) Add support for DMA_ATTR_NO_KERNEL_MAPPING to this new API instead
> >       of dma_alloc_attrs.  The initial difference with that flag is just
> >       that we allow highmem, but in the future we could also unmap this
> >       memory from the kernel linear mapping entirely on architectures
> >       where we can easily do that.
> 
> Mhm, why would we want to do this?

To avoid the CPU misspeculating into this memory.  For example NVMe SSDs
have a feature called host memory buffer that is a lot like your stolen
main ram for the GPU case.  We currently hand the SSD a
DMA_ATTR_NO_KERNEL_MAPPING allocation if it requests such a buffer.  If
possible we'd really like to make sure no speculative execution bug
(or intentional attacker with a kernel exploit for that matter) can easily
access that memory.
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  parent reply	other threads:[~2019-08-15 18:27 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-14 21:59 [PATCH 0/6] drm+dma: cache support for arm, etc Rob Clark
2019-08-14 21:59 ` [PATCH 1/6] arm64: export arch_sync_dma_for_*() Rob Clark
2019-08-14 21:59 ` [PATCH 2/6] mips: " Rob Clark
2019-08-14 21:59 ` [PATCH 3/6] powerpc: " Rob Clark
2019-08-14 21:59 ` [PATCH 4/6] arm: add arch_sync_dma_for_*() Rob Clark
2019-08-14 22:00 ` [PATCH 5/6] drm/msm: stop abusing DMA API Rob Clark
2019-08-14 22:00 ` [PATCH 6/6] drm/vgem: fix cache synchronization on arm/arm64 (take two) Rob Clark
     [not found] ` <20190814220011.26934-1-robdclark-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
2019-08-15  6:51   ` [PATCH 0/6] drm+dma: cache support for arm, etc Christoph Hellwig
     [not found]     ` <20190815065117.GA23761-jcswGhMUV9g@public.gmane.org>
2019-08-15 13:54       ` Rob Clark
     [not found]         ` <CAJs_Fx4bS64s7+xQqsead3N80ZQpofqegFQu+tT=b3wcGd_2pA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-08-15 17:53           ` Christoph Hellwig
     [not found]             ` <20190815175346.GA19839-jcswGhMUV9g@public.gmane.org>
2019-08-15 18:21               ` Koenig, Christian
     [not found]                 ` <e3f73b3c-49d5-3c19-dfff-0a24b4617e50-5C7GfCeVMHo@public.gmane.org>
2019-08-15 18:27                   ` Christoph Hellwig [this message]
2019-08-16 21:04             ` Rob Clark
     [not found]               ` <CAJs_Fx6am7TeDFSG=CcTT=4KwhqrZX_jnn56NaWcDkGVizuakg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-08-19  5:23                 ` Christoph Hellwig
     [not found]                   ` <20190819052337.GA16622-jcswGhMUV9g@public.gmane.org>
2019-08-19 14:39                     ` Rob Clark
  -- strict thread matches above, loose matches on Subject: below --
2019-08-15 18:48 Koenig, Christian
     [not found] ` <215e5cb7-0fcf-48db-a656-817054dde420-2ueSQiBKiTY7tOexoI0I+QC/G2K4zDHf@public.gmane.org>
2019-08-15 18:52   ` Christoph Hellwig

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