powerpc/mm: Differentiate between hugetlb and THP during page walk
We need to properly identify whether a hugepage is an explicit or
a transparent hugepage in follow_huge_addr(). We used to depend
on hugepage shift argument to do that. But in some case that can
result in wrong results. For ex:
On finding a transparent hugepage we set hugepage shift to PMD_SHIFT.
But we can end up clearing the thp pte, via pmdp_huge_get_and_clear.
We do prevent reusing the pfn page via the usage of
kick_all_cpus_sync(). But that happens after we updated the pte to 0.
Hence in follow_huge_addr() we can find hugepage shift set, but transparent
huge page check fail for a thp pte.
NOTE: We fixed a variant of this race against thp split in commit
691e95fd7396905a38d98919e9c150dbc3ea21a3
("powerpc/mm/thp: Make page table walk safe against thp split/collapse")
Without this patch, we may hit the BUG_ON(flags & FOLL_GET) in
follow_page_mask occasionally.
In the long term, we may want to switch ppc64 64k page size config to
enable CONFIG_ARCH_WANT_GENERAL_HUGETLB
Reported-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/arch/powerpc/include/asm/mmu-hash64.h b/arch/powerpc/include/asm/mmu-hash64.h
index a82f534..ba3342b 100644
--- a/arch/powerpc/include/asm/mmu-hash64.h
+++ b/arch/powerpc/include/asm/mmu-hash64.h
@@ -14,6 +14,7 @@
#include <asm/asm-compat.h>
#include <asm/page.h>
+#include <asm/bug.h>
/*
* This is necessary to get the definition of PGTABLE_RANGE which we
diff --git a/arch/powerpc/include/asm/pgtable-ppc64.h b/arch/powerpc/include/asm/pgtable-ppc64.h
index fa1dfb7..3245f2d 100644
--- a/arch/powerpc/include/asm/pgtable-ppc64.h
+++ b/arch/powerpc/include/asm/pgtable-ppc64.h
@@ -437,9 +437,9 @@
}
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
extern void hpte_do_hugepage_flush(struct mm_struct *mm, unsigned long addr,
pmd_t *pmdp, unsigned long old_pmd);
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
extern pmd_t pfn_pmd(unsigned long pfn, pgprot_t pgprot);
extern pmd_t mk_pmd(struct page *page, pgprot_t pgprot);
extern pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot);
@@ -479,6 +479,14 @@
}
extern int has_transparent_hugepage(void);
+#else
+static inline void hpte_do_hugepage_flush(struct mm_struct *mm,
+ unsigned long addr, pmd_t *pmdp,
+ unsigned long old_pmd)
+{
+
+ WARN(1, "%s called with THP disabled\n", __func__);
+}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
static inline int pmd_large(pmd_t pmd)
diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
index 0717693..b64b421 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h
@@ -259,15 +259,15 @@
#define has_transparent_hugepage() 0
#endif
pte_t *__find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea,
- unsigned *shift);
+ bool *is_thp, unsigned *shift);
static inline pte_t *find_linux_pte_or_hugepte(pgd_t *pgdir, unsigned long ea,
- unsigned *shift)
+ bool *is_thp, unsigned *shift)
{
if (!arch_irqs_disabled()) {
pr_info("%s called with irq enabled\n", __func__);
dump_stack();
}
- return __find_linux_pte_or_hugepte(pgdir, ea, shift);
+ return __find_linux_pte_or_hugepte(pgdir, ea, is_thp, shift);
}
#endif /* __ASSEMBLY__ */