[PATCH 2/5] MIPS: Add partial 32-bit huge page support

From: Paul Cercueil
Date: Mon Jul 15 2019 - 17:40:36 EST

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From: Daniel Silsby <dansilsby@xxxxxxxxx>

This adds initial support for huge pages to 32-bit MIPS systems.
Systems with extended addressing enabled (EVA,XPA,Alchemy/Netlogic)
are not yet supported.
With huge pages enabled, this implementation will increase page table
memory overhead to match that of a 64-bit MIPS system. However, the
cache-friendliness of page table walks is not affected significantly.

Signed-off-by: Daniel Silsby <dansilsby@xxxxxxxxx>
Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
---
arch/mips/include/asm/pgtable-32.h | 56 +++++++++++++++++++++++++---
arch/mips/include/asm/pgtable-bits.h | 4 +-
arch/mips/mm/pgtable-32.c | 20 ++++++++++
3 files changed, 73 insertions(+), 7 deletions(-)

diff --git a/arch/mips/include/asm/pgtable-32.h b/arch/mips/include/asm/pgtable-32.h
index 74afe8c76bdd..b0a78c9b6434 100644
--- a/arch/mips/include/asm/pgtable-32.h
+++ b/arch/mips/include/asm/pgtable-32.h
@@ -23,6 +23,24 @@
#include <asm/highmem.h>
#endif

+/*
+ * Regarding 32-bit MIPS huge page support (and the tradeoff it entails):
+ *
+ * We use the same huge page sizes as 64-bit MIPS. Assuming a 4KB page size,
+ * our 2-level table layout would normally have a PGD entry cover a contiguous
+ * 4MB virtual address region (pointing to a 4KB PTE page of 1,024 32-bit pte_t
+ * pointers, each pointing to a 4KB physical page). The problem is that 4MB,
+ * spanning both halves of a TLB EntryLo0,1 pair, requires 2MB hardware page
+ * support, not one of the standard supported sizes (1MB,4MB,16MB,...).
+ * To correct for this, when huge pages are enabled, we halve the number of
+ * pointers a PTE page holds, making its last half go to waste. Correspondingly,
+ * we double the number of PGD pages. Overall, page table memory overhead
+ * increases to match 64-bit MIPS, but PTE lookups remain CPU cache-friendly.
+ *
+ * NOTE: We don't yet support huge pages if extended-addressing is enabled
+ * (i.e. EVA, XPA, 36-bit Alchemy/Netlogic).
+ */
+
extern int temp_tlb_entry;

/*
@@ -44,7 +62,12 @@ extern int add_temporary_entry(unsigned long entrylo0, unsigned long entrylo1,
*/

/* PGDIR_SHIFT determines what a third-level page table entry can map */
-#define PGDIR_SHIFT (2 * PAGE_SHIFT + PTE_ORDER - PTE_T_LOG2)
+#if defined(CONFIG_MIPS_HUGE_TLB_SUPPORT) && !defined(CONFIG_PHYS_ADDR_T_64BIT)
+# define PGDIR_SHIFT (2 * PAGE_SHIFT + PTE_ORDER - PTE_T_LOG2 - 1)
+#else
+# define PGDIR_SHIFT (2 * PAGE_SHIFT + PTE_ORDER - PTE_T_LOG2)
+#endif
+
#define PGDIR_SIZE (1UL << PGDIR_SHIFT)
#define PGDIR_MASK (~(PGDIR_SIZE-1))

@@ -52,14 +75,23 @@ extern int add_temporary_entry(unsigned long entrylo0, unsigned long entrylo1,
* Entries per page directory level: we use two-level, so
* we don't really have any PUD/PMD directory physically.
*/
-#define __PGD_ORDER (32 - 3 * PAGE_SHIFT + PGD_T_LOG2 + PTE_T_LOG2)
+#if defined(CONFIG_MIPS_HUGE_TLB_SUPPORT) && !defined(CONFIG_PHYS_ADDR_T_64BIT)
+# define __PGD_ORDER (32 - 3 * PAGE_SHIFT + PGD_T_LOG2 + PTE_T_LOG2 + 1)
+#else
+# define __PGD_ORDER (32 - 3 * PAGE_SHIFT + PGD_T_LOG2 + PTE_T_LOG2)
+#endif
+
#define PGD_ORDER (__PGD_ORDER >= 0 ? __PGD_ORDER : 0)
#define PUD_ORDER aieeee_attempt_to_allocate_pud
#define PMD_ORDER 1
#define PTE_ORDER 0

#define PTRS_PER_PGD (USER_PTRS_PER_PGD * 2)
-#define PTRS_PER_PTE ((PAGE_SIZE << PTE_ORDER) / sizeof(pte_t))
+#if defined(CONFIG_MIPS_HUGE_TLB_SUPPORT) && !defined(CONFIG_PHYS_ADDR_T_64BIT)
+# define PTRS_PER_PTE ((PAGE_SIZE << PTE_ORDER) / sizeof(pte_t) / 2)
+#else
+# define PTRS_PER_PTE ((PAGE_SIZE << PTE_ORDER) / sizeof(pte_t))
+#endif

#define USER_PTRS_PER_PGD (0x80000000UL/PGDIR_SIZE)
#define FIRST_USER_ADDRESS 0UL
@@ -87,7 +119,7 @@ extern int add_temporary_entry(unsigned long entrylo0, unsigned long entrylo1,

extern void load_pgd(unsigned long pg_dir);

-extern pte_t invalid_pte_table[PAGE_SIZE/sizeof(pte_t)];
+extern pte_t invalid_pte_table[PTRS_PER_PTE];

/*
* Empty pgd/pmd entries point to the invalid_pte_table.
@@ -97,7 +129,19 @@ static inline int pmd_none(pmd_t pmd)
return pmd_val(pmd) == (unsigned long) invalid_pte_table;
}

-#define pmd_bad(pmd) (pmd_val(pmd) & ~PAGE_MASK)
+static inline int pmd_bad(pmd_t pmd)
+{
+#ifdef CONFIG_MIPS_HUGE_TLB_SUPPORT
+ /* pmd_huge(pmd) but inline */
+ if (unlikely(pmd_val(pmd) & _PAGE_HUGE))
+ return 0;
+#endif
+
+ if (unlikely(pmd_val(pmd) & ~PAGE_MASK))
+ return 1;
+
+ return 0;
+}

static inline int pmd_present(pmd_t pmd)
{
@@ -146,6 +190,7 @@ static inline pte_t pfn_pte(unsigned long pfn, pgprot_t prot)
#else
#define pte_pfn(x) ((unsigned long)((x).pte >> _PFN_SHIFT))
#define pfn_pte(pfn, prot) __pte(((unsigned long long)(pfn) << _PFN_SHIFT) | pgprot_val(prot))
+#define pfn_pmd(pfn, prot) __pmd(((unsigned long long)(pfn) << _PFN_SHIFT) | pgprot_val(prot))
#endif
#endif /* defined(CONFIG_PHYS_ADDR_T_64BIT) && defined(CONFIG_CPU_MIPS32) */

@@ -159,6 +204,7 @@ static inline pte_t pfn_pte(unsigned long pfn, pgprot_t prot)
#define pgd_offset_k(address) pgd_offset(&init_mm, address)

#define pgd_index(address) (((address) >> PGDIR_SHIFT) & (PTRS_PER_PGD-1))
+#define pmd_index(address) (((address) >> PMD_SHIFT) & (PTRS_PER_PMD-1))

/* to find an entry in a page-table-directory */
#define pgd_offset(mm, addr) ((mm)->pgd + pgd_index(addr))
diff --git a/arch/mips/include/asm/pgtable-bits.h b/arch/mips/include/asm/pgtable-bits.h
index f88a48cd68b2..f3b1efd23f21 100644
--- a/arch/mips/include/asm/pgtable-bits.h
+++ b/arch/mips/include/asm/pgtable-bits.h
@@ -110,7 +110,7 @@ enum pgtable_bits {
_PAGE_WRITE_SHIFT,
_PAGE_ACCESSED_SHIFT,
_PAGE_MODIFIED_SHIFT,
-#if defined(CONFIG_64BIT) && defined(CONFIG_MIPS_HUGE_TLB_SUPPORT)
+#if defined(CONFIG_MIPS_HUGE_TLB_SUPPORT)
_PAGE_HUGE_SHIFT,
#endif

@@ -132,7 +132,7 @@ enum pgtable_bits {
#define _PAGE_WRITE (1 << _PAGE_WRITE_SHIFT)
#define _PAGE_ACCESSED (1 << _PAGE_ACCESSED_SHIFT)
#define _PAGE_MODIFIED (1 << _PAGE_MODIFIED_SHIFT)
-#if defined(CONFIG_64BIT) && defined(CONFIG_MIPS_HUGE_TLB_SUPPORT)
+#if defined(CONFIG_MIPS_HUGE_TLB_SUPPORT)
# define _PAGE_HUGE (1 << _PAGE_HUGE_SHIFT)
#endif

diff --git a/arch/mips/mm/pgtable-32.c b/arch/mips/mm/pgtable-32.c
index e2a33adc0f29..6416a531a4c3 100644
--- a/arch/mips/mm/pgtable-32.c
+++ b/arch/mips/mm/pgtable-32.c
@@ -12,6 +12,7 @@
#include <asm/fixmap.h>
#include <asm/pgtable.h>
#include <asm/pgalloc.h>
+#include <asm/tlbflush.h>

void pgd_init(unsigned long page)
{
@@ -30,6 +31,25 @@ void pgd_init(unsigned long page)
}
}

+#if defined(CONFIG_TRANSPARENT_HUGEPAGE)
+pmd_t mk_pmd(struct page *page, pgprot_t prot)
+{
+ pmd_t pmd;
+
+ pmd_val(pmd) = (page_to_pfn(page) << _PFN_SHIFT) | pgprot_val(prot);
+
+ return pmd;
+}
+
+
+void set_pmd_at(struct mm_struct *mm, unsigned long addr,
+ pmd_t *pmdp, pmd_t pmd)
+{
+ *pmdp = pmd;
+ flush_tlb_all();
+}
+#endif /* defined(CONFIG_TRANSPARENT_HUGEPAGE) */
+
void __init pagetable_init(void)
{
unsigned long vaddr;
--
2.21.0.593.g511ec345e18

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