+ mm-cma-accept-memory-of-multi-range-cma-areas.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm/cma: accept memory of multi-range CMA areas
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-cma-accept-memory-of-multi-range-cma-areas.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-cma-accept-memory-of-multi-range-cma-areas.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Mike Rapoport (Microsoft)" <rppt@kernel.org>
Subject: mm/cma: accept memory of multi-range CMA areas
Date: Thu, 29 Oct 2026 12:18:37 +0200

Patch series "mm/cma: accept memory of CMA areas reserved with
memblock_reserve()", v1.

Pages of allocated CMA areas are released to the buddy allocator with
__free_pages(), which does not check for unaccepted memory.

This usually works because memblock accepts the memory it allocates.

However, multi-range CMA areas, used by hugetlb_cma, and fixed CMA areas
requested with cma=<size>@<base> are reserved with memblock_reserve() and
their memory is never accepted.

On TDX and SEV-SNP guests the first access to such a page is fatal.

To ease the backporting, each case is addressed by a separate patch:
- patch 1 accepts the memory of multi-range CMA areas
- patch 2 does the same for the fixed CMA areas

The second patch won't apply cleanly to 6.6 and 6.12, but I believe the
stable team LLMs will take care of that :)


This patch (of 2):

On systems with unaccepted memory, memblock allocations accept the
allocated range, but when cma_declare_contiguous_multi() uses open coded
allocation of multiple ranges, it reserves them with memblock_reserve()
and they are never accepted.

These pages are released to the buddy allocator by cma_activate_area()
with __free_pages() that does not check for unaccepted memory, so the
first access to such a page in a TDX or SEV-SNP guest is fatal.

Accept the memory of each range when it is reserved.

Link: https://lore.kernel.org/20261029-cma-multi-v1-0-2cbced8b5cb7@kernel.org
Link: https://lore.kernel.org/20261029-cma-multi-v1-1-2cbced8b5cb7@kernel.org
Fixes: c009da4258f9 ("mm, cma: support multiple contiguous ranges, if requested")
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: "Gupta, Pankaj" <pankaj.gupta@amd.com>
Cc: <stable@vger.kernel.org>
---

 mm/cma.c |    2 ++
 1 file changed, 2 insertions(+)

--- a/mm/cma.c~mm-cma-accept-memory-of-multi-range-cma-areas
+++ a/mm/cma.c
@@ -678,6 +678,8 @@ int __init cma_declare_contiguous_multi(
 			break;
 		}
 
+		accept_memory(mlp->base, size);
+
 		pr_debug("created region %d: %016llx - %016llx\n",
 		    nr, (u64)mlp->base, (u64)mlp->base + size);
 		cmrp = &cma->ranges[nr++];
_

Patches currently in -mm which might be from rppt@kernel.org are

mm-cma-accept-memory-of-multi-range-cma-areas.patch
mm-cma-accept-memory-of-cma-areas-reserved-at-a-fixed-address.patch