[PATCH V2] highmem: Fix kmap_to_page() for kmap_local_page() addresses

[ira . weiny]

From: Ira Weiny <ira.weiny@xxxxxxxxx>

kmap_to_page() is used to get the page for a virtual address which may
be kmap'ed.  Unfortunately, kmap_local_page() stores mappings in a
thread local array separate from kmap().  These mappings were not
checked by the call.

Check the kmap_local_page() mappings and return the page if found.

Because it is intended to remove kmap_to_page() add a warn on once to
the kmap checks to flag potential issues early.

NOTE Due to 32bit x86 use of kmap local in iomap atmoic, KMAP_LOCAL does
not require HIGHMEM to be set.  Therefore the support calls required a
new KMAP_LOCAL section to fix 0day build errors.

Cc: "Fabio M. De Francesco" <fmdefrancesco@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx>

---
Changes from V1:
	Fix 0day build errors.

I'm still working toward getting rid of kmap_to_page.[1]  But until then
this fix should be applied.

[1] https://lore.kernel.org/linux-mm/20221002002326.946620-1-ira.weiny@xxxxxxxxx/
---
 mm/highmem.c | 42 ++++++++++++++++++++++++++++++++----------
 1 file changed, 32 insertions(+), 10 deletions(-)

diff --git a/mm/highmem.c b/mm/highmem.c
index c707d7202d5f..529987b28205 100644
--- a/mm/highmem.c
+++ b/mm/highmem.c
@@ -30,6 +30,17 @@
 #include <asm/tlbflush.h>
 #include <linux/vmalloc.h>
 
+#ifdef CONFIG_KMAP_LOCAL
+static inline int kmap_local_calc_idx(int idx)
+{
+	return idx + KM_MAX_IDX * smp_processor_id();
+}
+
+#ifndef arch_kmap_local_map_idx
+#define arch_kmap_local_map_idx(idx, pfn)	kmap_local_calc_idx(idx)
+#endif
+#endif /* CONFIG_KMAP_LOCAL */
+
 /*
  * Virtual_count is not a pure "count".
  *  0 means that it is not mapped, and has not been mapped
@@ -142,14 +153,34 @@ pte_t *pkmap_page_table;
 
 struct page *__kmap_to_page(void *vaddr)
 {
+	unsigned long base = (unsigned long) vaddr & PAGE_MASK;
+	struct kmap_ctrl *kctrl = &current->kmap_ctrl;
 	unsigned long addr = (unsigned long)vaddr;
+	int i;
 
-	if (addr >= PKMAP_ADDR(0) && addr < PKMAP_ADDR(LAST_PKMAP)) {
+	/* kmap() mappings */
+	if (WARN_ON_ONCE(addr >= PKMAP_ADDR(0) &&
+			 addr < PKMAP_ADDR(LAST_PKMAP))) {
 		int i = PKMAP_NR(addr);
 
 		return pte_page(pkmap_page_table[i]);
 	}
 
+	/* kmap_local_page() mappings */
+	if (WARN_ON_ONCE(base >= __fix_to_virt(FIX_KMAP_END) &&
+			 base < __fix_to_virt(FIX_KMAP_BEGIN))) {
+		for (i = 0; i < kctrl->idx; i++) {
+			unsigned long base_addr;
+			int idx;
+
+			idx = arch_kmap_local_map_idx(i, pte_pfn(pteval));
+			base_addr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
+
+			if (base_addr == base)
+				return pte_page(kctrl->pteval[i]);
+		}
+	}
+
 	return virt_to_page(vaddr);
 }
 EXPORT_SYMBOL(__kmap_to_page);
@@ -462,10 +493,6 @@ static inline void kmap_local_idx_pop(void)
 # define arch_kmap_local_post_unmap(vaddr)		do { } while (0)
 #endif
 
-#ifndef arch_kmap_local_map_idx
-#define arch_kmap_local_map_idx(idx, pfn)	kmap_local_calc_idx(idx)
-#endif
-
 #ifndef arch_kmap_local_unmap_idx
 #define arch_kmap_local_unmap_idx(idx, vaddr)	kmap_local_calc_idx(idx)
 #endif
@@ -494,11 +521,6 @@ static inline bool kmap_high_unmap_local(unsigned long vaddr)
 	return false;
 }
 
-static inline int kmap_local_calc_idx(int idx)
-{
-	return idx + KM_MAX_IDX * smp_processor_id();
-}
-
 static pte_t *__kmap_pte;
 
 static pte_t *kmap_get_pte(unsigned long vaddr, int idx)
-- 
2.37.2