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Date:   Wed, 16 Jun 2021 20:25:19 -0700
From:   Eric Biggers <ebiggers@kernel.org>
To:     Satya Tangirala <satyat@google.com>
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH v3 07/10] mmc: handle error from blk_ksm_register()
Message-ID: <YMrAn7EkKkNVEjUW@sol.localdomain>
References: <20210604195900.2096121-1-satyat@google.com>
 <20210604195900.2096121-8-satyat@google.com>
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On Fri, Jun 04, 2021 at 07:58:57PM +0000, Satya Tangirala wrote:
> Handle any error from blk_ksm_register() in the callers. Previously,
> the callers ignored the return value because blk_ksm_register() wouldn't
> fail as long as the request_queue didn't have integrity support too, but
> as this is no longer the case, it's safer for the callers to just handle
> the return value appropriately.
> 
> Signed-off-by: Satya Tangirala <satyat@google.com>
> ---
>  drivers/mmc/core/crypto.c | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mmc/core/crypto.c b/drivers/mmc/core/crypto.c
> index 419a368f8402..cccd8c7d7e7a 100644
> --- a/drivers/mmc/core/crypto.c
> +++ b/drivers/mmc/core/crypto.c
> @@ -21,8 +21,17 @@ void mmc_crypto_set_initial_state(struct mmc_host *host)
>  
>  void mmc_crypto_setup_queue(struct request_queue *q, struct mmc_host *host)
>  {
> -	if (host->caps2 & MMC_CAP2_CRYPTO)
> -		blk_ksm_register(&host->ksm, q);
> +	if (host->caps2 & MMC_CAP2_CRYPTO) {
> +		/*
> +		 * This WARN_ON should never trigger since &host->ksm won't be
> +		 * "empty" (i.e. will support at least 1 crypto capability), an
> +		 * MMC device's request queue doesn't support integrity, and
> +		 * it also satisfies all the block layer constraints (i.e.
> +		 * supports SG gaps, doesn't have chunk sectors, has a
> +		 * sufficiently large supported max_segments per bio)
> +		 */
> +		WARN_ON(!blk_ksm_register(&host->ksm, q));
> +	}
>  }

There appear to be some MMC host drivers that set max_segments to 1, so this
explanation may not hold.  It may hold for every driver that actually supports
crypto, though.

- Eric