Re: [PATCH v10 10/12] poweprc: mm: Implement *_user_accessible_page() for ptes

Page table checking depends on architectures providing an
implementation of p{te,md,ud}_user_accessible_page. With
refactorisations made on powerpc/mm, the pte_access_permitted() and
similar methods verify whether a userland page is accessible with the
required permissions.

Since page table checking is the only user of
p{te,md,ud}_user_accessible_page(), implement these for all platforms,
using some of the same preliminay checks taken by pte_access_permitted()
on that platform.

Since Commit 8e9bd41e4ce1 ("powerpc/nohash: Replace pte_user() by pte_read()")
pte_user() is no longer required to be present on all platforms as it
may be equivalent to or implied by pte_read(). Hence implementations are
specialised.

Signed-off-by: Rohan McLure <redacted>
---
v9: New implementation
v10: Let book3s/64 use pte_user(), but otherwise default other platforms
to using the address provided with the call to infer whether it is a
user page or not. pmd/pud variants will warn on all other platforms, as
they should not be used for user page mappings
---
  arch/powerpc/include/asm/book3s/64/pgtable.h | 19 ++++++++++++++
  arch/powerpc/include/asm/pgtable.h           | 26 ++++++++++++++++++++
  2 files changed, 45 insertions(+)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 382724c5e872..ca765331e21d 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h

@@ -538,6 +538,12 @@ static inline bool pte_access_permitted(pte_t pte, bool write)
  	return arch_pte_access_permitted(pte_val(pte), write, 0);
  }
  
+#define pte_user_accessible_page pte_user_accessible_page
+static inline bool pte_user_accessible_page(pte_t pte, unsigned long addr)
+{
+	return pte_present(pte) && pte_user(pte);
+}
+
  /*
   * Conversion functions: convert a page and protection to a page entry,
   * and a page entry and page directory to the page they refer to.

@@ -881,6 +887,7 @@ static inline int pud_present(pud_t pud)
  
  extern struct page *pud_page(pud_t pud);
  extern struct page *pmd_page(pmd_t pmd);
+

  static inline pte_t pud_pte(pud_t pud)
  {
  	return __pte_raw(pud_raw(pud));

@@ -926,6 +933,12 @@ static inline bool pud_access_permitted(pud_t pud, bool write)
  	return pte_access_permitted(pud_pte(pud), write);
  }
  
+#define pud_user_accessible_page pud_user_accessible_page
+static inline bool pud_user_accessible_page(pud_t pud, unsigned long addr)
+{
+	return pte_user_accessible_page(pud_pte(pud), addr);
+}
+

  #define __p4d_raw(x)	((p4d_t) { __pgd_raw(x) })
  static inline __be64 p4d_raw(p4d_t x)
  {

@@ -1091,6 +1104,12 @@ static inline bool pmd_access_permitted(pmd_t pmd, bool write)
  	return pte_access_permitted(pmd_pte(pmd), write);
  }
  
+#define pmd_user_accessible_page pmd_user_accessible_page
+static inline bool pmd_user_accessible_page(pmd_t pmd, unsigned long addr)
+{
+	return pte_user_accessible_page(pmd_pte(pmd), addr);
+}

+
  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
  extern pmd_t pfn_pmd(unsigned long pfn, pgprot_t pgprot);
  extern pud_t pfn_pud(unsigned long pfn, pgprot_t pgprot);

diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h
index 13f661831333..3741a63fb82e 100644
--- a/arch/powerpc/include/asm/pgtable.h
+++ b/arch/powerpc/include/asm/pgtable.h

@@ -227,6 +227,32 @@ static inline int pud_pfn(pud_t pud)
  }
  #endif
  
+#ifndef pte_user_accessible_page
+#define pte_user_accessible_page pte_user_accessible_page
+static inline bool pte_user_accessible_page(pte_t pte, unsigned long addr)
+{
+	return pte_present(pte) && !is_kernel_addr(addr);
+}
+#endif