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Date: Mon, 9 Mar 2026 16:02:33 +0200
From: Leon Romanovsky <leon@kernel.org>
To: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Jiri Pirko <jiri@resnulli.us>, dri-devel@lists.freedesktop.org,
	linaro-mm-sig@lists.linaro.org, iommu@lists.linux.dev,
	linux-media@vger.kernel.org, sumit.semwal@linaro.org,
	benjamin.gaignard@collabora.com, Brian.Starkey@arm.com,
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	aneesh.kumar@kernel.org, suzuki.poulose@arm.com,
	steven.price@arm.com, thomas.lendacky@amd.com, john.allen@amd.com,
	ashish.kalra@amd.com, suravee.suthikulpanit@amd.com,
	linux-coco@lists.linux.dev
Subject: Re: [PATCH net-next v3 1/2] dma-mapping: introduce
 DMA_ATTR_CC_DECRYPTED for pre-decrypted memory
Message-ID: <20260309140233.GW12611@unreal>
References: <20260305123641.164164-1-jiri@resnulli.us>
 <20260305123641.164164-2-jiri@resnulli.us>
 <20260308101948.GO12611@unreal>
 <20260309131530.GJ1687929@ziepe.ca>
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In-Reply-To: <20260309131530.GJ1687929@ziepe.ca>

On Mon, Mar 09, 2026 at 10:15:30AM -0300, Jason Gunthorpe wrote:
> On Sun, Mar 08, 2026 at 12:19:48PM +0200, Leon Romanovsky wrote:
> 
> > > +/*
> > > + * DMA_ATTR_CC_DECRYPTED: Indicates memory that has been explicitly decrypted
> > > + * (shared) for confidential computing guests. The caller must have
> > > + * called set_memory_decrypted(). A struct page is required.
> > > + */
> > > +#define DMA_ATTR_CC_DECRYPTED	(1UL << 12)
> > 
> > While adding the new attribute is fine, I would expect additional checks in
> > dma_map_phys() to ensure the attribute cannot be misused. For example,
> > WARN_ON(attrs & (DMA_ATTR_CC_DECRYPTED | DMA_ATTR_MMIO)), along with a check
> > that we are taking the direct path only.
> 
> DECRYPYED and MMIO is something that needs to work, VFIO (inside a
> TVM) should be using that combination.

So this sentence "A struct page is required" from the comment above is
not accurate.

Thanks

> 
> Jason