linux-kernel - Re: [PATCH 1/3] dm integrity: do not filter algos with CRYPTO_ALG_ALLOCATES

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Message-ID: <Z7RGwot_t0RLc3-F@gondor.apana.org.au>
Date: Tue, 18 Feb 2025 16:37:22 +0800
From: Herbert Xu <herbert@...dor.apana.org.au>
To: Meenakshi Aggarwal <meenakshi.aggarwal@....com>
Cc: Giovanni Cabiddu <giovanni.cabiddu@...el.com>,
	Eric Biggers <ebiggers@...nel.org>,
	"agk@...hat.com" <agk@...hat.com>,
	"snitzer@...nel.org" <snitzer@...nel.org>,
	"linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
	"dm-devel@...hat.com" <dm-devel@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"qat-linux@...el.com" <qat-linux@...el.com>,
	"heinzm@...hat.com" <heinzm@...hat.com>,
	Horia Geanta <horia.geanta@....com>, Varun Sethi <V.Sethi@....com>,
	Pankaj Gupta <pankaj.gupta@....com>,
	Gaurav Jain <gaurav.jain@....com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	Iuliana Prodan <iuliana.prodan@....com>,
	Fiona Trahe <fiona.trahe@...el.com>
Subject: Re: [PATCH 1/3] dm integrity: do not filter algos with
 CRYPTO_ALG_ALLOCATES_MEMORY

On Wed, Feb 07, 2024 at 06:22:06AM +0000, Meenakshi Aggarwal wrote:
> 
> What are your plans for this change?

I finally have a solution for you.

The answer is to use a software fallback.  As software fallbacks
do not need to allocate memory, they can be used in an OOM situation
and you fail to allocate memory in the driver with GFP_ATOMIC.

This can either be done using the existing shash interface through
SHASH_DESC_ON_STACK, or with my new hash interface where you can
use HASH_REQUEST_ON_STACK.

Once you have implemented this fallback strategy you may remove
the CRYPTO_ALG_ALLOCATES_MEMORY flag from your driver.

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