From: "Lendacky, Thomas" <Thomas.Lendacky@amd.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Dave Hansen <dave.hansen@linux.intel.com>,
Lianbo Jiang <lijiang@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
"x86@kernel.org" <x86@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"iommu@lists.linux-foundation.org"
<iommu@lists.linux-foundation.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Andy Lutomirski <luto@kernel.org>,
"H . Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Robin Murphy <robin.murphy@arm.com>,
Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH] dma-direct: Force unencrypted DMA under SME for certain DMA masks
Date: Wed, 24 Jul 2019 16:42:35 +0000 [thread overview]
Message-ID: <acee0a74-77fc-9c81-087b-ce55abf87bd4@amd.com> (raw)
In-Reply-To: <20190724155530.hlingpcirjcf2ljg@box>
On 7/24/19 10:55 AM, Kirill A. Shutemov wrote:
> 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?
Not really... it's the way DMA_BIT_MASK works vs bit numbering. Let's say
that sme_me_mask has bit 47 set. __ffs64 returns 47 and DMA_BIT_MASK(47)
will generate a mask without bit 47 set (0x7fffffffffff). So the check
will catch anything that does not support at least 48-bit DMA.
Thanks,
Tom
>
>> + }
>> +
>> + return false;
>> +}
>
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next prev parent reply other threads:[~2019-07-24 16:42 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-10 19:01 [PATCH] dma-direct: Force unencrypted DMA under SME for certain DMA masks Lendacky, Thomas
2019-07-11 10:05 ` Christoph Hellwig
2019-07-11 12:18 ` Thomas Gleixner
2019-07-11 12:16 ` Thomas Gleixner
2019-07-24 15:55 ` Kirill A. Shutemov
2019-07-24 16:42 ` Lendacky, Thomas [this message]
2019-07-24 17:06 ` Robin Murphy
2019-07-24 17:34 ` Lendacky, Thomas
2019-07-24 18:11 ` Kirill A. Shutemov
2019-07-24 18:30 ` Lendacky, Thomas
2019-07-24 18:40 ` Kirill A. Shutemov
2019-07-24 18:49 ` Lendacky, Thomas
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