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powerpc/mm: fix wrong addr_pfn tracking in compound vmemmap population

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vmemmap_populate_compound_pages() uses addr_pfn to determine the PFN
offset within a compound page and to decide whether the current vmemmap
slot should be populated as a head page mapping or should reuse a tail
page mapping.

However, addr_pfn is advanced manually in parallel with addr.  The loop
itself progresses in vmemmap address space, so each PAGE_SIZE step in addr
covers PAGE_SIZE / sizeof(struct page) struct page slots.  Since addr_pfn
is compared against nr_pages in data-PFN units, it should advance by the
same number of PFNs.  The existing manual increments do not match that and
therefore do not reliably track the PFN corresponding to the current addr.

As a result, pfn_offset can be computed from the wrong PFN and the code
can make the head/tail decision for the wrong compound-page position.

Fix this by deriving addr_pfn directly from the current vmemmap address
instead of carrying it as loop state.

Link: https://lore.kernel.org/20260612035903.2468601-4-songmuchun@bytedance.com
Fixes: f2b79c0d79 ("powerpc/book3s64/radix: add support for vmemmap optimization for radix")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: David Hildenbrand <david@kernel.org>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Mike Rapoport (Microsoft) <rppt@kernel.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oscar Salvador (SUSE) <osalvador@kernel.org>
Cc: Usama Arif <usama.arif@linux.dev>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Muchun Song 2026-06-12 11:58:47 +08:00 committed by Andrew Morton
parent 6e25c6a9c7
commit 89a4ae3276
1 changed files with 1 additions and 6 deletions
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7
arch/powerpc/mm/book3s64/radix_pgtable.c
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@ -1314,7 +1314,6 @@ int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn,
* covering out both edges.
*/
unsigned long addr;
unsigned long addr_pfn = start_pfn;
unsigned long next;
pgd_t *pgd;
p4d_t *p4d;
@ -1335,7 +1334,6 @@ int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn,
if (pmd_leaf(READ_ONCE(*pmd))) {
/* existing huge mapping. Skip the range */
addr_pfn += (PMD_SIZE >> PAGE_SHIFT);
next = pmd_addr_end(addr, end);
continue;
}
@ -1348,11 +1346,11 @@ int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn,
* page whose VMEMMAP_RESERVE_NR pages were mapped and
* this request fall in those pages.
*/
addr_pfn += 1;
next = addr + PAGE_SIZE;
continue;
} else {
unsigned long nr_pages = pgmap_vmemmap_nr(pgmap);
unsigned long addr_pfn = page_to_pfn((struct page *)addr);
unsigned long pfn_offset = addr_pfn - ALIGN_DOWN(addr_pfn, nr_pages);
pte_t *tail_page_pte;
@ -1376,7 +1374,6 @@ int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn,
if (!pte)
return -ENOMEM;
addr_pfn += 2;
next = addr + 2 * PAGE_SIZE;
continue;
}
@ -1392,7 +1389,6 @@ int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn,
return -ENOMEM;
vmemmap_verify(pte, node, addr, addr + PAGE_SIZE);
addr_pfn += 1;
next = addr + PAGE_SIZE;
continue;
}
@ -1402,7 +1398,6 @@ int __meminit vmemmap_populate_compound_pages(unsigned long start_pfn,
return -ENOMEM;
vmemmap_verify(pte, node, addr, addr + PAGE_SIZE);
addr_pfn += 1;
next = addr + PAGE_SIZE;
continue;
}