linux-kernel - Re: [PATCH] dma-direct: Force unencrypted DMA under SME for certain DMA masks

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Date:   Thu, 11 Jul 2019 14:16:48 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Lendacky, Thomas" <Thomas.Lendacky@....com>
cc:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>, Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Lianbo Jiang <lijiang@...hat.com>
Subject: Re: [PATCH] dma-direct: Force unencrypted DMA under SME for certain
 DMA masks

On Wed, 10 Jul 2019, Lendacky, Thomas wrote:

> From: Tom Lendacky <thomas.lendacky@....com>
> 
> If a device doesn't support DMA to a physical address that includes the
> encryption bit (currently bit 47, so 48-bit DMA), then the DMA must
> occur to unencrypted memory. SWIOTLB is used to satisfy that requirement
> if an IOMMU is not active (enabled or configured in passthrough mode).
> 
> However, commit fafadcd16595 ("swiotlb: don't dip into swiotlb pool for
> coherent allocations") modified the coherent allocation support in SWIOTLB
> to use the DMA direct coherent allocation support. When an IOMMU is not
> active, this resulted in dma_alloc_coherent() failing for devices that
> didn't support DMA addresses that included the encryption bit.
> 
> Addressing this requires changes to the force_dma_unencrypted() function
> in kernel/dma/direct.c. Since the function is now non-trivial and SME/SEV
> specific, update the DMA direct support to add an arch override for the
> force_dma_unencrypted() function. The arch override is selected when
> CONFIG_AMD_MEM_ENCRYPT is set. The arch override function resides in the
> arch/x86/mm/mem_encrypt.c file and forces unencrypted DMA when either SEV
> is active or SME is active and the device does not support DMA to physical
> addresses that include the encryption bit.
> 
> Fixes: fafadcd16595 ("swiotlb: don't dip into swiotlb pool for coherent allocations")
> Suggested-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
> 
> Based on tree git://git.infradead.org/users/hch/dma-mapping.git for-next
> 
>  arch/x86/Kconfig          |  1 +

For the x86 parts:

Acked-by: Thomas Gleixner <tglx@...utronix.de>