linux-kernel - Re: [PATCH 3/4 RESEND] crypto: octeontx2: Fix address alignment on CN10K A0/A1 and OcteonTX2

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Message-ID: <CAAeCc_mKDq2jSM+yZ816nx_BPsFSWiCjEswfuu9HBzXrv+V+WQ@mail.gmail.com>
Date: Tue, 20 May 2025 10:04:21 +0530
From: Bharat Bhushan <bharatb.linux@...il.com>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: Bharat Bhushan <bbhushan2@...vell.com>, bbrezillon@...nel.org, arno@...isbad.org, 
	schalla@...vell.com, davem@...emloft.net, giovanni.cabiddu@...el.com, 
	linux@...blig.org, linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org
Subject: Re: [PATCH 3/4 RESEND] crypto: octeontx2: Fix address alignment on
 CN10K A0/A1 and OcteonTX2

On Mon, May 19, 2025 at 1:05 PM Herbert Xu <herbert@...dor.apana.org.au> wrote:
>
> On Mon, May 19, 2025 at 11:47:18AM +0530, Bharat Bhushan wrote:
> >
> > > > +     /* Allocate extra memory for SG and response address alignment */
> > > > +     total_mem_len = ALIGN(info_len, OTX2_CPT_DPTR_RPTR_ALIGN) + dlen;
> >
> > This add extra memory for 8-byte (OTX2_CPT_DPTR_RPTR_ALIGN) alignment
> >
> > > > +     total_mem_len = ALIGN(total_mem_len, OTX2_CPT_RES_ADDR_ALIGN) +
> > > > +                      sizeof(union otx2_cpt_res_s);
> >
> > This add extra memory for 32-byte (OTX2_CPT_RES_ADDR_ALIGN))
> > In case not observed,  OTX2_CPT_RES_ADDR_ALIGN is not the same as
> > OTX2_CPT_DPTR_RPTR_ALIGN.
>
> But it doesn't do that.  Look, assume that total_mem_len is 64,
> then ALIGN(64, 32) will still be 64.  You're not adding any extra
> space for the alignment padding.
>
> OTOH, kmalloc can return something that has a page offset of 8,
> and you will need 24 extra bytes in your structure to make it
> align at 32.
>
> Now of course if you're very lucky, and total_mem_len starts out
> at 8, then it would work but that's purely by chance.

Thanks for explaining, will change in the next version.

Thanks
-Bharat

>
> 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