[PATCH v4 03/19] powerpc/mm: Fix wrong addr_pfn tracking in compound vmemmap population

[Muchun Song <songmuchun@bytedance.com>]

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.

Fixes: f2b79c0d7968 ("powerpc/book3s64/radix: add support for vmemmap optimization for radix")
Cc: stable@vger.kernel.org
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Oscar Salvador <osalvador@suse.de>
Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

---
v3->v4:
- Add Cc: stable@vger.kernel.org (suggested by Ritesh Harjani)
- Collect Reviewed-by from Ritesh Harjani
---
 arch/powerpc/mm/book3s64/radix_pgtable.c | 7 +------
 1 file changed, 1 insertion(+), 6 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
index 10aced261cff..cf692b2b5f7b 100644
--- a/arch/powerpc/mm/book3s64/radix_pgtable.c
+++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
@@ -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;
 		}
-- 
2.54.0