From: Aneesh Kumar K.V <aneesh.kumar@kernel.org>
To: Tom Lendacky <thomas.lendacky@amd.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
iommu@lists.linux.dev
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@kernel.org>, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>, "H . Peter Anvin" <hpa@zytor.com>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Mostafa Saleh <smostafa@google.com>,
Alexander.Deucher@amd.com, Vasant.Hegde@amd.com,
Timo Witte <timo.witte@gmail.com>,
Alexey Kardashevskiy <aik@amd.com>
Subject: Re: [PATCH] x86/mm: Don't force unencrypted DMA for IOMMU-backed devices
Date: Tue, 15 Sep 2026 14:20:15 +0530 [thread overview]
Message-ID: <yq5aqziu2914.fsf@kernel.org> (raw)
In-Reply-To: <df4209bb-0bfb-4f19-9de1-2b03148846fc@amd.com>
Tom Lendacky <thomas.lendacky@amd.com> writes:
> On 9/8/26 06:32, Aneesh Kumar K.V (Arm) wrote:
[ ... 39 lines skipped ... ]
>>
>> @@ -30,7 +31,7 @@ bool force_dma_unencrypted(struct device *dev)
>> * device does not support DMA to addresses that include the
>> * encryption mask.
>> */
>> - if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT)) {
>> + if (cc_platform_has(CC_ATTR_HOST_MEM_ENCRYPT) && !use_dma_iommu(dev)) {
>
> When this support was originally added many years ago, this function was
> not called if an IOMMU was active and generating IOVAs. So if this
> function is now called even when an IOMMU is performing the DMA mapping,
> then this is appropriate. Although, it would seem that if an IOMMU is
> performing the mapping and this function is still being called, checking
> use_dma_iommu(dev) and exiting early from force_dma_unencrypted() at the
> very beginning is more appropriate, right?
>
I don't think that is correct for a confidential guest with a stage-1 IOMMU.
> @Alexey, would that impact your TIO/TDISP support at all?
>
-aneesh
prev parent reply other threads:[~2026-09-15 8:50 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20260908113247eucas1p12e67fcdf50573da0c0fac36cee4b06e9@eucas1p1.samsung.com>
2026-09-08 11:32 ` Aneesh Kumar K.V (Arm)
2026-09-08 14:24 ` Michael Kelley
2026-09-08 14:31 ` Marek Szyprowski
2026-09-11 8:32 ` Marek Szyprowski
2026-09-14 13:17 ` Tom Lendacky
2026-09-15 8:50 ` Aneesh Kumar K.V [this message]
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