[Xen-devel] [PATCH v1 1/4] kasan: introduce set_pmd_early_shadow()

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

It is incorrect to call pmd_populate_kernel() multiple times for the
same page table. Xen notices it during kasan_populate_early_shadow():

    (XEN) mm.c:3222:d155v0 mfn 3704b already pinned

This happens for kasan_early_shadow_pte when USE_SPLIT_PTE_PTLOCKS is
enabled. Fix this by introducing set_pmd_early_shadow() which calls
pmd_populate_kernel() only once and uses set_pmd() afterwards.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
RFC --> v1:
- New patch
---
 mm/kasan/init.c | 25 +++++++++++++++++--------
 1 file changed, 17 insertions(+), 8 deletions(-)

diff --git a/mm/kasan/init.c b/mm/kasan/init.c
index ce45c491ebcd..a4077320777f 100644
--- a/mm/kasan/init.c
+++ b/mm/kasan/init.c
@@ -81,6 +81,19 @@ static inline bool kasan_early_shadow_page_entry(pte_t pte)
        return pte_page(pte) == virt_to_page(lm_alias(kasan_early_shadow_page));
 }
 
+static inline void set_pmd_early_shadow(pmd_t *pmd)
+{
+       static bool pmd_populated = false;
+       pte_t *early_shadow = lm_alias(kasan_early_shadow_pte);
+
+       if (likely(pmd_populated)) {
+               set_pmd(pmd, __pmd(__pa(early_shadow) | _PAGE_TABLE));
+       } else {
+               pmd_populate_kernel(&init_mm, pmd, early_shadow);
+               pmd_populated = true;
+       }
+}
+
 static __init void *early_alloc(size_t size, int node)
 {
        void *ptr = memblock_alloc_try_nid(size, size, __pa(MAX_DMA_ADDRESS),
@@ -120,8 +133,7 @@ static int __ref zero_pmd_populate(pud_t *pud, unsigned 
long addr,
                next = pmd_addr_end(addr, end);
 
                if (IS_ALIGNED(addr, PMD_SIZE) && end - addr >= PMD_SIZE) {
-                       pmd_populate_kernel(&init_mm, pmd,
-                                       lm_alias(kasan_early_shadow_pte));
+                       set_pmd_early_shadow(pmd);
                        continue;
                }
 
@@ -157,8 +169,7 @@ static int __ref zero_pud_populate(p4d_t *p4d, unsigned 
long addr,
                        pud_populate(&init_mm, pud,
                                        lm_alias(kasan_early_shadow_pmd));
                        pmd = pmd_offset(pud, addr);
-                       pmd_populate_kernel(&init_mm, pmd,
-                                       lm_alias(kasan_early_shadow_pte));
+                       set_pmd_early_shadow(pmd);
                        continue;
                }
 
@@ -198,8 +209,7 @@ static int __ref zero_p4d_populate(pgd_t *pgd, unsigned 
long addr,
                        pud_populate(&init_mm, pud,
                                        lm_alias(kasan_early_shadow_pmd));
                        pmd = pmd_offset(pud, addr);
-                       pmd_populate_kernel(&init_mm, pmd,
-                                       lm_alias(kasan_early_shadow_pte));
+                       set_pmd_early_shadow(pmd);
                        continue;
                }
 
@@ -271,8 +281,7 @@ int __ref kasan_populate_early_shadow(const void 
*shadow_start,
                        pud_populate(&init_mm, pud,
                                        lm_alias(kasan_early_shadow_pmd));
                        pmd = pmd_offset(pud, addr);
-                       pmd_populate_kernel(&init_mm, pmd,
-                                       lm_alias(kasan_early_shadow_pte));
+                       set_pmd_early_shadow(pmd);
                        continue;
                }
 
-- 
2.17.1


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