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

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Date:   Wed, 24 Jul 2019 18:55:30 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
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>,
        Thomas Gleixner <tglx@...utronix.de>,
        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, Jul 10, 2019 at 07:01:19PM +0000, Lendacky, Thomas wrote:
> @@ -351,6 +355,32 @@ bool sev_active(void)
>  }
>  EXPORT_SYMBOL(sev_active);
>  
> +/* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED */
> +bool force_dma_unencrypted(struct device *dev)
> +{
> +	/*
> +	 * For SEV, all DMA must be to unencrypted addresses.
> +	 */
> +	if (sev_active())
> +		return true;
> +
> +	/*
> +	 * For SME, all DMA must be to unencrypted addresses if the
> +	 * device does not support DMA to addresses that include the
> +	 * encryption mask.
> +	 */
> +	if (sme_active()) {
> +		u64 dma_enc_mask = DMA_BIT_MASK(__ffs64(sme_me_mask));
> +		u64 dma_dev_mask = min_not_zero(dev->coherent_dma_mask,
> +						dev->bus_dma_mask);
> +
> +		if (dma_dev_mask <= dma_enc_mask)
> +			return true;

Hm. What is wrong with the dev mask being equal to enc mask? IIUC, it
means that device mask is wide enough to cover encryption bit, doesn't it?

> +	}
> +
> +	return false;
> +}

-- 
 Kirill A. Shutemov