linux-kernel - Re: [RFC Part1 PATCH v3 12/17] x86/mm: DMA support for SEV memory encryption

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Date:   Thu, 17 Aug 2017 14:35:25 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...e.de>, Brijesh Singh <brijesh.singh@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-efi@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Piotr Luc <piotr.luc@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Laura Abbott <labbott@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jonathan Corbet <corbet@....net>,
        Dave Airlie <airlied@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [RFC Part1 PATCH v3 12/17] x86/mm: DMA support for SEV memory
 encryption



On 8/6/2017 10:48 PM, Borislav Petkov wrote:
> On Mon, Jul 24, 2017 at 02:07:52PM -0500, Brijesh Singh wrote:
>> From: Tom Lendacky <thomas.lendacky@....com>
>>
>> DMA access to memory mapped as encrypted while SEV is active can not be
>> encrypted during device write or decrypted during device read.
> 
> Yeah, definitely rewrite that sentence.

Heh, yup.

> 
>> In order
>> for DMA to properly work when SEV is active, the SWIOTLB bounce buffers
>> must be used.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
>> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
>> ---
>>   arch/x86/mm/mem_encrypt.c | 86 +++++++++++++++++++++++++++++++++++++++++++++++
>>   lib/swiotlb.c             |  5 +--
>>   2 files changed, 89 insertions(+), 2 deletions
> 
> ...
> 
>> @@ -202,6 +280,14 @@ void __init mem_encrypt_init(void)
>>   	/* Call into SWIOTLB to update the SWIOTLB DMA buffers */
>>   	swiotlb_update_mem_attributes();
>>   
>> +	/*
>> +	 * With SEV, DMA operations cannot use encryption. New DMA ops
>> +	 * are required in order to mark the DMA areas as decrypted or
>> +	 * to use bounce buffers.
>> +	 */
>> +	if (sev_active())
>> +		dma_ops = &sme_dma_ops;
> 
> Well, we do differentiate between SME and SEV and the check is
> sev_active but the ops are called sme_dma_ops. Call them sev_dma_ops
> instead for less confusion.

Yup, will do.

Thanks,
Tom

>