arch/tile: support 4KB page size as well as 64KB

The Tilera architecture traditionally supports 64KB page sizes
to improve TLB utilization and improve performance when the
hardware is being used primarily to run a single application.

For more generic server scenarios, it can be beneficial to run
with 4KB page sizes, so this commit allows that to be specified
(by modifying the arch/tile/include/hv/pagesize.h header).

As part of this change, we also re-worked the PTE management
slightly so that PTE writes all go through a __set_pte() function
where we can do some additional validation.  The set_pte_order()
function was eliminated since the "order" argument wasn't being used.

One bug uncovered was in the PCI DMA code, which wasn't properly
flushing the specified range.  This was benign with 64KB pages,
but with 4KB pages we were getting some larger flushes wrong.

The per-cpu memory reservation code also needed updating to
conform with the newer percpu stuff; before it always chose 64KB,
and that was always correct, but with 4KB granularity we now have
to pay closer attention and reserve the amount of memory that will
be requested when the percpu code starts allocating.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>

4 files changed, 144 insertions, 47 deletions

diff --git a/arch/tile/mm/homecache.c b/arch/tile/mm/homecache.c
index f344f4f..cbe6f4f 100644
--- a/arch/tile/mm/homecache.c
+++ b/arch/tile/mm/homecache.c
@@ -412,7 +412,7 @@ void homecache_change_page_home(struct page *page, int order, int home)
 		pte_t *ptep = virt_to_pte(NULL, kva);
 		pte_t pteval = *ptep;
 		BUG_ON(!pte_present(pteval) || pte_huge(pteval));
-		*ptep = pte_set_home(pteval, home);
+		__set_pte(ptep, pte_set_home(pteval, home));
 	}
 }
 
diff --git a/arch/tile/mm/init.c b/arch/tile/mm/init.c
index f89ed5d..d6e87fd 100644
--- a/arch/tile/mm/init.c
+++ b/arch/tile/mm/init.c
@@ -53,18 +53,6 @@
 
 #include "migrate.h"
 
-/*
- * We could set FORCE_MAX_ZONEORDER to "(HPAGE_SHIFT - PAGE_SHIFT + 1)"
- * in the Tile Kconfig, but this generates configure warnings.
- * Do it here and force people to get it right to compile this file.
- * The problem is that with 4KB small pages and 16MB huge pages,
- * the default value doesn't allow us to group enough small pages
- * together to make up a huge page.
- */
-#if CONFIG_FORCE_MAX_ZONEORDER < HPAGE_SHIFT - PAGE_SHIFT + 1
-# error "Change FORCE_MAX_ZONEORDER in arch/tile/Kconfig to match page size"
-#endif
-
 #define clear_pgd(pmdptr) (*(pmdptr) = hv_pte(0))
 
 #ifndef __tilegx__
@@ -962,11 +950,7 @@ struct kmem_cache *pgd_cache;
 
 void __init pgtable_cache_init(void)
 {
-	pgd_cache = kmem_cache_create("pgd",
-				PTRS_PER_PGD*sizeof(pgd_t),
-				PTRS_PER_PGD*sizeof(pgd_t),
-				0,
-				NULL);
+	pgd_cache = kmem_cache_create("pgd", SIZEOF_PGD, SIZEOF_PGD, 0, NULL);
 	if (!pgd_cache)
 		panic("pgtable_cache_init(): Cannot create pgd cache");
 }
diff --git a/arch/tile/mm/migrate_32.S b/arch/tile/mm/migrate_32.S
index f738765..ac01a7c 100644
--- a/arch/tile/mm/migrate_32.S
+++ b/arch/tile/mm/migrate_32.S
@@ -18,6 +18,7 @@
 #include <linux/linkage.h>
 #include <linux/threads.h>
 #include <asm/page.h>
+#include <asm/thread_info.h>
 #include <asm/types.h>
 #include <asm/asm-offsets.h>
 #include <hv/hypervisor.h>
diff --git a/arch/tile/mm/pgtable.c b/arch/tile/mm/pgtable.c
index 2c850d9..1a2b36f 100644
--- a/arch/tile/mm/pgtable.c
+++ b/arch/tile/mm/pgtable.c
@@ -142,6 +142,76 @@ pte_t *_pte_offset_map(pmd_t *dir, unsigned long address)
 }
 #endif
 
+/**
+ * shatter_huge_page() - ensure a given address is mapped by a small page.
+ *
+ * This function converts a huge PTE mapping kernel LOWMEM into a bunch
+ * of small PTEs with the same caching.  No cache flush required, but we
+ * must do a global TLB flush.
+ *
+ * Any caller that wishes to modify a kernel mapping that might
+ * have been made with a huge page should call this function,
+ * since doing so properly avoids race conditions with installing the
+ * newly-shattered page and then flushing all the TLB entries.
+ *
+ * @addr: Address at which to shatter any existing huge page.
+ */
+void shatter_huge_page(unsigned long addr)
+{
+	pgd_t *pgd;
+	pud_t *pud;
+	pmd_t *pmd;
+	unsigned long flags = 0;  /* happy compiler */
+#ifdef __PAGETABLE_PMD_FOLDED
+	struct list_head *pos;
+#endif
+
+	/* Get a pointer to the pmd entry that we need to change. */
+	addr &= HPAGE_MASK;
+	BUG_ON(pgd_addr_invalid(addr));
+	BUG_ON(addr < PAGE_OFFSET);  /* only for kernel LOWMEM */
+	pgd = swapper_pg_dir + pgd_index(addr);
+	pud = pud_offset(pgd, addr);
+	BUG_ON(!pud_present(*pud));
+	pmd = pmd_offset(pud, addr);
+	BUG_ON(!pmd_present(*pmd));
+	if (!pmd_huge_page(*pmd))
+		return;
+
+	/*
+	 * Grab the pgd_lock, since we may need it to walk the pgd_list,
+	 * and since we need some kind of lock here to avoid races.
+	 */
+	spin_lock_irqsave(&pgd_lock, flags);
+	if (!pmd_huge_page(*pmd)) {
+		/* Lost the race to convert the huge page. */
+		spin_unlock_irqrestore(&pgd_lock, flags);
+		return;
+	}
+
+	/* Shatter the huge page into the preallocated L2 page table. */
+	pmd_populate_kernel(&init_mm, pmd,
+			    get_prealloc_pte(pte_pfn(*(pte_t *)pmd)));
+
+#ifdef __PAGETABLE_PMD_FOLDED
+	/* Walk every pgd on the system and update the pmd there. */
+	list_for_each(pos, &pgd_list) {
+		pmd_t *copy_pmd;
+		pgd = list_to_pgd(pos) + pgd_index(addr);
+		pud = pud_offset(pgd, addr);
+		copy_pmd = pmd_offset(pud, addr);
+		__set_pmd(copy_pmd, *pmd);
+	}
+#endif
+
+	/* Tell every cpu to notice the change. */
+	flush_remote(0, 0, NULL, addr, HPAGE_SIZE, HPAGE_SIZE,
+		     cpu_possible_mask, NULL, 0);
+
+	/* Hold the lock until the TLB flush is finished to avoid races. */
+	spin_unlock_irqrestore(&pgd_lock, flags);
+}
+
 /*
  * List of all pgd's needed so it can invalidate entries in both cached
  * and uncached pgd's. This is essentially codepath-based locking
@@ -184,9 +254,9 @@ static void pgd_ctor(pgd_t *pgd)
 	BUG_ON(((u64 *)swapper_pg_dir)[pgd_index(MEM_USER_INTRPT)] != 0);
 #endif
 
-	clone_pgd_range(pgd + KERNEL_PGD_INDEX_START,
-			swapper_pg_dir + KERNEL_PGD_INDEX_START,
-			KERNEL_PGD_PTRS);
+	memcpy(pgd + KERNEL_PGD_INDEX_START,
+	       swapper_pg_dir + KERNEL_PGD_INDEX_START,
+	       KERNEL_PGD_PTRS * sizeof(pgd_t));
 
 	pgd_list_add(pgd);
 	spin_unlock_irqrestore(&pgd_lock, flags);
@@ -220,8 +290,11 @@ void pgd_free(struct mm_struct *mm, pgd_t *pgd)
 
 struct page *pte_alloc_one(struct mm_struct *mm, unsigned long address)
 {
-	gfp_t flags = GFP_KERNEL|__GFP_REPEAT|__GFP_ZERO|__GFP_COMP;
+	gfp_t flags = GFP_KERNEL|__GFP_REPEAT|__GFP_ZERO;
 	struct page *p;
+#if L2_USER_PGTABLE_ORDER > 0
+	int i;
+#endif
 
 #ifdef CONFIG_HIGHPTE
 	flags |= __GFP_HIGHMEM;
@@ -231,6 +304,18 @@ struct page *pte_alloc_one(struct mm_struct *mm, unsigned long address)
 	if (p == NULL)
 		return NULL;
 
+#if L2_USER_PGTABLE_ORDER > 0
+	/*
+	 * Make every page have a page_count() of one, not just the first.
+	 * We don't use __GFP_COMP since it doesn't look like it works
+	 * correctly with tlb_remove_page().
+	 */
+	for (i = 1; i < L2_USER_PGTABLE_PAGES; ++i) {
+		init_page_count(p+i);
+		inc_zone_page_state(p+i, NR_PAGETABLE);
+	}
+#endif
+
 	pgtable_page_ctor(p);
 	return p;
 }
@@ -242,8 +327,15 @@ struct page *pte_alloc_one(struct mm_struct *mm, unsigned long address)
  */
 void pte_free(struct mm_struct *mm, struct page *p)
 {
+	int i;
+
 	pgtable_page_dtor(p);
-	__free_pages(p, L2_USER_PGTABLE_ORDER);
+	__free_page(p);
+
+	for (i = 1; i < L2_USER_PGTABLE_PAGES; ++i) {
+		__free_page(p+i);
+		dec_zone_page_state(p+i, NR_PAGETABLE);
+	}
 }
 
 void __pte_free_tlb(struct mmu_gather *tlb, struct page *pte,
@@ -252,8 +344,12 @@ void __pte_free_tlb(struct mmu_gather *tlb, struct page *pte,
 	int i;
 
 	pgtable_page_dtor(pte);
-	for (i = 0; i < L2_USER_PGTABLE_PAGES; ++i)
+	tlb_remove_page(tlb, pte);
+
+	for (i = 1; i < L2_USER_PGTABLE_PAGES; ++i) {
 		tlb_remove_page(tlb, pte + i);
+		dec_zone_page_state(pte + i, NR_PAGETABLE);
+	}
 }
 
 #ifndef __tilegx__
@@ -335,35 +431,51 @@ int get_remote_cache_cpu(pgprot_t prot)
 	return x + y * smp_width;
 }
 
-void set_pte_order(pte_t *ptep, pte_t pte, int order)
+/*
+ * Convert a kernel VA to a PA and homing information.
+ */
+int va_to_cpa_and_pte(void *va, unsigned long long *cpa, pte_t *pte)
 {
-	unsigned long pfn = pte_pfn(pte);
-	struct page *page = pfn_to_page(pfn);
+	struct page *page = virt_to_page(va);
+	pte_t null_pte = { 0 };
 
-	/* Update the home of a PTE if necessary */
-	pte = pte_set_home(pte, page_home(page));
+	*cpa = __pa(va);
+
+	/* Note that this is not writing a page table, just returning a pte. */
+	*pte = pte_set_home(null_pte, page_home(page));
+
+	return 0; /* return non-zero if not hfh? */
+}
+EXPORT_SYMBOL(va_to_cpa_and_pte);
 
+void __set_pte(pte_t *ptep, pte_t pte)
+{
 #ifdef __tilegx__
 	*ptep = pte;
 #else
-	/*
-	 * When setting a PTE, write the high bits first, then write
-	 * the low bits.  This sets the "present" bit only after the
-	 * other bits are in place.  If a particular PTE update
-	 * involves transitioning from one valid PTE to another, it
-	 * may be necessary to call set_pte_order() more than once,
-	 * transitioning via a suitable intermediate state.
-	 * Note that this sequence also means that if we are transitioning
-	 * from any migrating PTE to a non-migrating one, we will not
-	 * see a half-updated PTE with the migrating bit off.
-	 */
-#if HV_PTE_INDEX_PRESENT >= 32 || HV_PTE_INDEX_MIGRATING >= 32
-# error Must write the present and migrating bits last
-#endif
-	((u32 *)ptep)[1] = (u32)(pte_val(pte) >> 32);
-	barrier();
-	((u32 *)ptep)[0] = (u32)(pte_val(pte));
-#endif
+# if HV_PTE_INDEX_PRESENT >= 32 || HV_PTE_INDEX_MIGRATING >= 32
+#  error Must write the present and migrating bits last
+# endif
+	if (pte_present(pte)) {
+		((u32 *)ptep)[1] = (u32)(pte_val(pte) >> 32);
+		barrier();
+		((u32 *)ptep)[0] = (u32)(pte_val(pte));
+	} else {
+		((u32 *)ptep)[0] = (u32)(pte_val(pte));
+		barrier();
+		((u32 *)ptep)[1] = (u32)(pte_val(pte) >> 32);
+	}
+#endif /* __tilegx__ */
+}
+
+void set_pte(pte_t *ptep, pte_t pte)
+{
+	struct page *page = pfn_to_page(pte_pfn(pte));
+
+	/* Update the home of a PTE if necessary */
+	pte = pte_set_home(pte, page_home(page));
+
+	__set_pte(ptep, pte);
 }
 
 /* Can this mm load a PTE with cached_priority set? */