Re: [PATCH V4 06/18] powerpc/mm: Switch book3s 64 with 64K page size to 4 level page table

Paul Mackerras [off-list ref] writes:

On Tue, Feb 23, 2016 at 10:18:08AM +0530, Aneesh Kumar K.V wrote:

quoted

This is needed so that we can support both hash and radix page table
using single kernel. Radix kernel uses a 4 level table.

Signed-off-by: Aneesh Kumar K.V <redacted>
---
 arch/powerpc/Kconfig                          |  1 +
 arch/powerpc/include/asm/book3s/64/hash-4k.h  | 33 +--------------------------
 arch/powerpc/include/asm/book3s/64/hash-64k.h | 20 +++++++++-------
 arch/powerpc/include/asm/book3s/64/hash.h     | 11 +++++++++
 arch/powerpc/include/asm/book3s/64/pgtable.h  | 25 +++++++++++++++++++-
 arch/powerpc/include/asm/pgalloc-64.h         | 28 ++++++++++++++++++++---
 arch/powerpc/include/asm/pgtable-types.h      | 13 +++++++----
 arch/powerpc/mm/init_64.c                     | 21 ++++++++++++-----
 8 files changed, 97 insertions(+), 55 deletions(-)

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 9faa18c4f3f7..599329332613 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig

@@ -303,6 +303,7 @@ config ZONE_DMA32
 config PGTABLE_LEVELS
 	int
 	default 2 if !PPC64
+	default 4 if PPC_BOOK3S_64
 	default 3 if PPC_64K_PAGES
 	default 4

Why not just "default 4"?  Why do we still need the if PPC_BOOK3S_64
line at all?

You are suggesting remove that PPC_64K_PAGES line right ? I was not sure
about other platforms that use 64K pages.

[...]

quoted

diff --git a/arch/powerpc/include/asm/book3s/64/hash.h b/arch/powerpc/include/asm/book3s/64/hash.h
index ef9bd68f7e6d..d0ee6fcef823 100644
--- a/arch/powerpc/include/asm/book3s/64/hash.h
+++ b/arch/powerpc/include/asm/book3s/64/hash.h

@@ -235,6 +235,7 @@
 #define __pgtable_ptr_val(ptr)	__pa(ptr)
 
 #define pgd_index(address) (((address) >> (PGDIR_SHIFT)) & (PTRS_PER_PGD - 1))
+#define pud_index(address) (((address) >> (PUD_SHIFT)) & (PTRS_PER_PUD - 1))
 #define pmd_index(address) (((address) >> (PMD_SHIFT)) & (PTRS_PER_PMD - 1))
 #define pte_index(address) (((address) >> (PAGE_SHIFT)) & (PTRS_PER_PTE - 1))
 

@@ -363,8 +364,18 @@ static inline void __ptep_set_access_flags(pte_t *ptep, pte_t entry)
 	:"cc");
 }
 
+static inline int pgd_bad(pgd_t pgd)
+{
+	return (pgd_val(pgd) == 0);
+}
+
 #define __HAVE_ARCH_PTE_SAME
 #define pte_same(A,B)	(((pte_val(A) ^ pte_val(B)) & ~_PAGE_HPTEFLAGS) == 0)
+static inline unsigned long pgd_page_vaddr(pgd_t pgd)
+{
+	return (unsigned long)__va(pgd_val(pgd) & ~PGD_MASKED_BITS);
+}
+
 
 /* Generic accessors to PTE bits */
 static inline int pte_write(pte_t pte)		{ return !!(pte_val(pte) & _PAGE_RW);}

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 7482f69117b6..77d3ce05798e 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h

@@ -106,6 +106,26 @@ static inline void pgd_set(pgd_t *pgdp, unsigned long val)
 	*pgdp = __pgd(val);
 }
 
+static inline void pgd_clear(pgd_t *pgdp)
+{
+	*pgdp = __pgd(0);
+}
+
+#define pgd_none(pgd)		(!pgd_val(pgd))
+#define pgd_present(pgd)	(!pgd_none(pgd))
+
+static inline pte_t pgd_pte(pgd_t pgd)
+{
+	return __pte(pgd_val(pgd));
+}
+
+static inline pgd_t pte_pgd(pte_t pte)
+{
+	return __pgd(pte_val(pte));
+}
+
+extern struct page *pgd_page(pgd_t pgd);

Why did you put pgd_bad() and pgd_page_vaddr() in hash.h, but
pgd_clear(), pgd_none, pgd_present etc. in pgtable.h?  Why split them
between two headers rather than putting them all in the same header?

Any page table operation that involved PTE bit position I am moving to
hash.h with the expectation that we will have to put a conditional call
in there. Functions like pgd_none and pgd_clear don't use bit
positions.

-aneesh