linux-kernel - Re: crypto API and GFP

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Date:   Wed, 10 Jun 2020 08:02:23 -0400 (EDT)
From:   Mikulas Patocka <mpatocka@...hat.com>
To:     Herbert Xu <herbert@...dor.apana.org.au>
cc:     "David S. Miller" <davem@...emloft.net>,
        linux-crypto@...r.kernel.org, Mike Snitzer <msnitzer@...hat.com>,
        Milan Broz <mbroz@...hat.com>, dm-devel@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: crypto API and GFP_ATOMIC

On Wed, 10 Jun 2020, Herbert Xu wrote:

> On Tue, Jun 09, 2020 at 01:11:05PM -0400, Mikulas Patocka wrote:
> >
> > Do you have another idea how to solve this problem?
> 
> I think the better approach would be to modify the drivers to not
> allocate any memory.  In general, any memory needed by the driver
> to fulfil a request *should* be allocated within the crypto request
> object.  That's why we have the reqsize field to indicate how much
> memory could be needed per request.
> 
> Thanks,

Yes, fixing the drivers would be the best - but you can hardly find any 
person who has all the crypto hardware and who is willing to rewrite all 
the drivers for it.

Another possibility - I was thinking about setting 
CRYPTO_TFM_REQ_MAY_SLEEP in dm-crypt and calling the crypto function under 
memalloc_noio_save. But there are some drivers that do GFP_ATOMIC 
allocation regardless of CRYPTO_TFM_REQ_MAY_SLEEP.

Mikulas