linux-kernel - Re: [RFC v3 -next] cma: Enforce non-zero pageblock_order during cma_init_reserved

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Message-Id: <20241112225902.f20215e5015f4d7cdf502302@linux-foundation.org>
Date: Tue, 12 Nov 2024 22:59:02 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
Cc: linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org, Sourabh Jain
 <sourabhjain@...ux.ibm.com>, Hari Bathini <hbathini@...ux.ibm.com>, Zi Yan
 <ziy@...dia.com>, David Hildenbrand <david@...hat.com>,
 "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>, Mahesh J
 Salgaonkar <mahesh@...ux.ibm.com>, Michael Ellerman <mpe@...erman.id.au>,
 Madhavan Srinivasan <maddy@...ux.ibm.com>, "Aneesh Kumar K . V"
 <aneesh.kumar@...nel.org>, Donet Tom <donettom@...ux.vnet.ibm.com>, LKML
 <linux-kernel@...r.kernel.org>, Sachin P Bappalige <sachinpb@...ux.ibm.com>
Subject: Re: [RFC v3 -next] cma: Enforce non-zero pageblock_order during
 cma_init_reserved_mem()

On Fri, 11 Oct 2024 20:26:09 +0530 "Ritesh Harjani (IBM)" <ritesh.list@...il.com> wrote:

> cma_init_reserved_mem() checks base and size alignment with
> CMA_MIN_ALIGNMENT_BYTES. However, some users might call this during
> early boot when pageblock_order is 0.

This sounds like "some users" are in error.  Please tell us precisely
which users we're talking about here.

Is there a startup ordering issue here?  It feels like a bad idea to
work around callers' flaws within the callee.

Please also describe the userspace-visible effects of this.  Because it
might be the case that we will want to backport any fix into earlier
kernels, and we shouldn't do that until we know how those kernels will
benefit.

And to aid all of this, please attempt to identify a Fixes: target, to
aid others in identifying which kernel version(s) need patching.

Please answer all the above in the next (non-RFC!) version's changelog.

Meanwhile, I'll queue up this version for some testing.

Thanks.