linux-kernel - [PATCH v4 -next] cma: Enforce non-zero pageblock_order during cma_init_reserved

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Message-ID: <e274344b44d5f80fa54c52f530387257fe99ec65.1731505681.git.ritesh.list@gmail.com>
Date: Wed, 13 Nov 2024 19:49:54 +0530
From: "Ritesh Harjani (IBM)" <ritesh.list@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
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>,
	"Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
	Anshuman Khandual <anshuman.khandual@....com>
Subject: [PATCH v4 -next] cma: Enforce non-zero pageblock_order during cma_init_reserved_mem()

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. That means if base and size does
not have pageblock_order alignment, it can cause functional failures
during cma activate area.

So let's enforce pageblock_order to be non-zero during
cma_init_reserved_mem() to catch such wrong usages.

Acked-by: David Hildenbrand <david@...hat.com>
Acked-by: Zi Yan <ziy@...dia.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@....com>
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
---
RFCv3 -> v4:
1. Dropped RFC tagged as requested by Andrew.
2. Updated the changelog & added background as requested by Andrew [RFCv3]
3. Added acked-by and RBs tags.
4. Small commit msg update.
5. No functional changes.
[RFCv3]: https://lore.kernel.org/all/20241112225902.f20215e5015f4d7cdf502302@linux-foundation.org/

Background -
============
1. This was seen with fadump on PowerPC which was calling
   cma_init_reserved_mem() before the pageblock_order was initialized.
   This is now fixed in the fadump on PowerPC itself. The details of that
   can be found in the patch including the userspace-visible effect of the issue [1].
2. However it was also decided that we should add a stronger enforcement check
   within cma_init_reserved_mem() to catch such wrong usages [2]. Hence this
   patch. This is ok to be in -next and there is no "Fixes" tag required for
   this patch.

[1]: https://lore.kernel.org/all/3ae208e48c0d9cefe53d2dc4f593388067405b7d.1729146153.git.ritesh.list@gmail.com/
[2]: https://lore.kernel.org/all/83eb128e-4f06-4725-a843-a4563f246a44@redhat.com/

 mm/cma.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/mm/cma.c b/mm/cma.c
index 3e9724716bad..36d753e7a0bf 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -182,6 +182,15 @@ int __init cma_init_reserved_mem(phys_addr_t base, phys_addr_t size,
 	if (!size || !memblock_is_region_reserved(base, size))
 		return -EINVAL;

+	/*
+	 * CMA uses CMA_MIN_ALIGNMENT_BYTES as alignment requirement which
+	 * needs pageblock_order to be initialized. Let's enforce it.
+	 */
+	if (!pageblock_order) {
+		pr_err("pageblock_order not yet initialized. Called during early boot?\n");
+		return -EINVAL;
+	}
+
 	/* ensure minimal alignment required by mm core */
 	if (!IS_ALIGNED(base | size, CMA_MIN_ALIGNMENT_BYTES))
 		return -EINVAL;
--
2.46.0