RE: [PATCH] crypto: inside-secure - Fix corruption on not fully coherent systems

["Van Leeuwen, Pascal" <pvanleeuwen@rambus.com>]

> -----Original Message-----
> From: Herbert Xu <herbert@gondor.apana.org.au>
> Sent: Friday, September 18, 2020 10:01 AM
> To: Van Leeuwen, Pascal <pvanleeuwen@rambus.com>
> Cc: linux-crypto@vger.kernel.org; antoine.tenart@bootlin.com; davem@davemloft.net; Ard Biesheuvel <ardb@kernel.org>
> Subject: Re: [PATCH] crypto: inside-secure - Fix corruption on not fully coherent systems
>
> <<< External Email >>>
> On Fri, Sep 18, 2020 at 07:42:35AM +0000, Van Leeuwen, Pascal wrote:
> >
> > Actually, that is what we did as a _quick hack_ initially, but:
> >
> > First of all, it's not only about the L1 cacheline size. It's about the worst case cache
> > line size in the path all the way from the CPU to the actual memory interface.
> >
> > Second, cache line sizes may differ from system to system. So it's not actually
> > a constant at all (unless you compile the driver specifically for 1 target system).
>
> Can this alignment exceed ARCH_DMA_MINALIGN? If not then the
> macro CRYPTO_MINALIGN should cover it.
>
I don't know. I'm not familiar with that macro and I have not been able to dig up any
clear description on what it should convey.

Based on the name, I might be inclined to think yes, but based on many definitions
I've seen in header files, I would say no. Because it's often just an alias for the L1
cacheline size, which may not be the largest cacheline for _some_ systems.

In any case, aligning to the worst cache cacheline for a CPU architecture may mean
you end up wasting a lot of space on a system with a much smaller cacheline.

> Cheers,
> --
> Email: Herbert Xu <herbert@gondor.apana.org.au>
> Home Page: http://gondor.apana.org.au/~herbert/
> PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Regards,
Pascal van Leeuwen
Silicon IP Architect Multi-Protocol Engines, Rambus Security
Rambus ROTW Holding BV
+31-73 6581953

Note: The Inside Secure/Verimatrix Silicon IP team was recently acquired by Rambus.
Please be so kind to update your e-mail address book with my new e-mail address.


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