Re: [RFC PATCH crypto] AES: Add support to Intel AES-NI instructions

[Huang Ying <ying.huang@intel.com>]

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On Wed, 2008-12-17 at 09:26 +0800, Herbert Xu wrote:
> Huang Ying <ying.huang@intel.com> wrote:
> >
> > f. if TS is clear, then use x86_64 implementation. Otherwise if
> > user-space has touched the FPU, we save the state, if not then simply
> > clear TS.
> 
> Well I'd rather avoid using the x86_64 implementation ever because
> unless the chip guys have really screwed up we should be looking at
> a difference of at least a factor of 10.
> 
> BTW I wasn't very clear in the original email.  You'd only do the
> asynchronous operation for CBC/ECB.  For the simple AES case I
> suppose we'll just have to stick to the x86_64 fallback.  This'll
> really suck for disk encryption but I guess you could always add
> an LRW/XTS mode to your code.

It seems that asynchronous operations are only provided in blkcipher
level not cipher level. So the situation may be as follow:

- Now an AES core block algorithm is implemented with AES-NI as
CRYPTO_ALG_TYPE_CIPHER, which can benefit all modes (CBC, LRW, etc). But
because it seems that there is no asynchronous interface for
CRYPTO_ALG_TYPE_CIPHER, the AES core block algorithm can not use a
thread to defer real operations.

- To take full advantage of AES-NI pipeline implementation, at least
"cbc(aes)", "ecb(aes)" and "ctr(aes)" should be implemented as
CRYPTO_ALG_TYPE_ABLKCIPHER. So a thread can be used to defer real
operation upon soft_irq.

Because the combination that kernel process context FPU usage + soft_irq
AES usage is fairly rare, I think the above combination is acceptable.
That is,

- In AES core block algorithm implementation with AES-NI, use x86_64
implementation for the combination above.

- In "cbc(aes)", "ecb(aes)" and "ctr(aes)", use thread deferring for the
combination above.

Best Regards,
Huang Ying


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