[S390] lockless get_user_pages_fast()

Implement get_user_pages_fast without locking in the fastpath on s390.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/Kconfig

@@ -101,6 +101,7 @@ config S390
 	select HAVE_KERNEL_BZIP2
 	select HAVE_KERNEL_LZMA
 	select HAVE_KERNEL_LZO
+	select HAVE_GET_USER_PAGES_FAST
 	select ARCH_INLINE_SPIN_TRYLOCK
 	select ARCH_INLINE_SPIN_TRYLOCK_BH
 	select ARCH_INLINE_SPIN_LOCK

arch/s390/include/asm/pgalloc.h

@@ -21,9 +21,11 @@
 
 unsigned long *crst_table_alloc(struct mm_struct *, int);
 void crst_table_free(struct mm_struct *, unsigned long *);
+void crst_table_free_rcu(struct mm_struct *, unsigned long *);
 
 unsigned long *page_table_alloc(struct mm_struct *);
 void page_table_free(struct mm_struct *, unsigned long *);
+void page_table_free_rcu(struct mm_struct *, unsigned long *);
 void disable_noexec(struct mm_struct *, struct task_struct *);
 
 static inline void clear_table(unsigned long *s, unsigned long val, size_t n)
@@ -176,4 +178,6 @@ static inline void pmd_populate(struct mm_struct *mm,
 #define pte_free_kernel(mm, pte) page_table_free(mm, (unsigned long *) pte)
 #define pte_free(mm, pte) page_table_free(mm, (unsigned long *) pte)
 
+extern void rcu_table_freelist_finish(void);
+
 #endif /* _S390_PGALLOC_H */

arch/s390/include/asm/pgtable.h

@@ -316,6 +316,7 @@ extern unsigned long VMALLOC_START;
 
 /* Bits in the segment table entry */
 #define _SEGMENT_ENTRY_ORIGIN	0x7fffffc0UL	/* page table origin	    */
+#define _SEGMENT_ENTRY_RO	0x200	/* page protection bit		    */
 #define _SEGMENT_ENTRY_INV	0x20	/* invalid segment table entry	    */
 #define _SEGMENT_ENTRY_COMMON	0x10	/* common segment bit		    */
 #define _SEGMENT_ENTRY_PTL	0x0f	/* page table length		    */

arch/s390/include/asm/tlb.h

@@ -64,17 +64,18 @@ static inline void tlb_flush_mmu(struct mmu_gather *tlb,
 	if (!tlb->fullmm && (tlb->nr_ptes > 0 || tlb->nr_pxds < TLB_NR_PTRS))
 		__tlb_flush_mm(tlb->mm);
 	while (tlb->nr_ptes > 0)
-		pte_free(tlb->mm, tlb->array[--tlb->nr_ptes]);
+		page_table_free_rcu(tlb->mm, tlb->array[--tlb->nr_ptes]);
 	while (tlb->nr_pxds < TLB_NR_PTRS)
-		/* pgd_free frees the pointer as region or segment table */
-		pgd_free(tlb->mm, tlb->array[tlb->nr_pxds++]);
+		crst_table_free_rcu(tlb->mm, tlb->array[tlb->nr_pxds++]);
 }
 
 static inline void tlb_finish_mmu(struct mmu_gather *tlb,
 				  unsigned long start, unsigned long end)
 {
 	tlb_flush_mmu(tlb, start, end);
 
+	rcu_table_freelist_finish();
+
 	/* keep the page table cache within bounds */
 	check_pgt_cache();
 
@@ -103,7 +104,7 @@ static inline void pte_free_tlb(struct mmu_gather *tlb, pgtable_t pte,
 		if (tlb->nr_ptes >= tlb->nr_pxds)
 			tlb_flush_mmu(tlb, 0, 0);
 	} else
-		pte_free(tlb->mm, pte);
+		page_table_free(tlb->mm, (unsigned long *) pte);
 }
 
 /*
@@ -124,7 +125,7 @@ static inline void pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
 		if (tlb->nr_ptes >= tlb->nr_pxds)
 			tlb_flush_mmu(tlb, 0, 0);
 	} else
-		pmd_free(tlb->mm, pmd);
+		crst_table_free(tlb->mm, (unsigned long *) pmd);
 #endif
 }
 
@@ -146,7 +147,7 @@ static inline void pud_free_tlb(struct mmu_gather *tlb, pud_t *pud,
 		if (tlb->nr_ptes >= tlb->nr_pxds)
 			tlb_flush_mmu(tlb, 0, 0);
 	} else
-		pud_free(tlb->mm, pud);
+		crst_table_free(tlb->mm, (unsigned long *) pud);
 #endif
 }
 

arch/s390/mm/Makefile

@@ -3,6 +3,6 @@
 #
 
 obj-y	 := init.o fault.o extmem.o mmap.o vmem.o pgtable.o maccess.o \
-	    page-states.o
+	    page-states.o gup.o
 obj-$(CONFIG_CMM) += cmm.o
 obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o

arch/s390/mm/gup.c

@@ -0,0 +1,225 @@
+/*
+ *  Lockless get_user_pages_fast for s390
+ *
+ *  Copyright IBM Corp. 2010
+ *  Author(s): Martin Schwidefsky <schwidefsky@de.ibm.com>
+ */
+#include <linux/sched.h>
+#include <linux/mm.h>
+#include <linux/hugetlb.h>
+#include <linux/vmstat.h>
+#include <linux/pagemap.h>
+#include <linux/rwsem.h>
+#include <asm/pgtable.h>
+
+/*
+ * The performance critical leaf functions are made noinline otherwise gcc
+ * inlines everything into a single function which results in too much
+ * register pressure.
+ */
+static inline int gup_pte_range(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
+		unsigned long end, int write, struct page **pages, int *nr)
+{
+	unsigned long mask, result;
+	pte_t *ptep, pte;
+	struct page *page;
+
+	result = write ? 0 : _PAGE_RO;
+	mask = result | _PAGE_INVALID | _PAGE_SPECIAL;
+
+	ptep = ((pte_t *) pmd_deref(pmd)) + pte_index(addr);
+	do {
+		pte = *ptep;
+		barrier();
+		if ((pte_val(pte) & mask) != result)
+			return 0;
+		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
+		page = pte_page(pte);
+		if (!page_cache_get_speculative(page))
+			return 0;
+		if (unlikely(pte_val(pte) != pte_val(*ptep))) {
+			put_page(page);
+			return 0;
+		}
+		pages[*nr] = page;
+		(*nr)++;
+
+	} while (ptep++, addr += PAGE_SIZE, addr != end);
+
+	return 1;
+}
+
+static inline int gup_huge_pmd(pmd_t *pmdp, pmd_t pmd, unsigned long addr,
+		unsigned long end, int write, struct page **pages, int *nr)
+{
+	unsigned long mask, result;
+	struct page *head, *page;
+	int refs;
+
+	result = write ? 0 : _SEGMENT_ENTRY_RO;
+	mask = result | _SEGMENT_ENTRY_INV;
+	if ((pmd_val(pmd) & mask) != result)
+		return 0;
+	VM_BUG_ON(!pfn_valid(pmd_val(pmd) >> PAGE_SHIFT));
+
+	refs = 0;
+	head = pmd_page(pmd);
+	page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
+	do {
+		VM_BUG_ON(compound_head(page) != head);
+		pages[*nr] = page;
+		(*nr)++;
+		page++;
+		refs++;
+	} while (addr += PAGE_SIZE, addr != end);
+
+	if (!page_cache_add_speculative(head, refs)) {
+		*nr -= refs;
+		return 0;
+	}
+
+	if (unlikely(pmd_val(pmd) != pmd_val(*pmdp))) {
+		*nr -= refs;
+		while (refs--)
+			put_page(head);
+	}
+
+	return 1;
+}
+
+
+static inline int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr,
+		unsigned long end, int write, struct page **pages, int *nr)
+{
+	unsigned long next;
+	pmd_t *pmdp, pmd;
+
+	pmdp = (pmd_t *) pudp;
+#ifdef CONFIG_64BIT
+	if ((pud_val(pud) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R3)
+		pmdp = (pmd_t *) pud_deref(pud);
+	pmdp += pmd_index(addr);
+#endif
+	do {
+		pmd = *pmdp;
+		barrier();
+		next = pmd_addr_end(addr, end);
+		if (pmd_none(pmd))
+			return 0;
+		if (unlikely(pmd_huge(pmd))) {
+			if (!gup_huge_pmd(pmdp, pmd, addr, next,
+					  write, pages, nr))
+				return 0;
+		} else if (!gup_pte_range(pmdp, pmd, addr, next,
+					  write, pages, nr))
+			return 0;
+	} while (pmdp++, addr = next, addr != end);
+
+	return 1;
+}
+
+static inline int gup_pud_range(pgd_t *pgdp, pgd_t pgd, unsigned long addr,
+		unsigned long end, int write, struct page **pages, int *nr)
+{
+	unsigned long next;
+	pud_t *pudp, pud;
+
+	pudp = (pud_t *) pgdp;
+#ifdef CONFIG_64BIT
+	if ((pgd_val(pgd) & _REGION_ENTRY_TYPE_MASK) == _REGION_ENTRY_TYPE_R2)
+		pudp = (pud_t *) pgd_deref(pgd);
+	pudp += pud_index(addr);
+#endif
+	do {
+		pud = *pudp;
+		barrier();
+		next = pud_addr_end(addr, end);
+		if (pud_none(pud))
+			return 0;
+		if (!gup_pmd_range(pudp, pud, addr, next, write, pages, nr))
+			return 0;
+	} while (pudp++, addr = next, addr != end);
+
+	return 1;
+}
+
+/**
+ * get_user_pages_fast() - pin user pages in memory
+ * @start:	starting user address
+ * @nr_pages:	number of pages from start to pin
+ * @write:	whether pages will be written to
+ * @pages:	array that receives pointers to the pages pinned.
+ *		Should be at least nr_pages long.
+ *
+ * Attempt to pin user pages in memory without taking mm->mmap_sem.
+ * If not successful, it will fall back to taking the lock and
+ * calling get_user_pages().
+ *
+ * Returns number of pages pinned. This may be fewer than the number
+ * requested. If nr_pages is 0 or negative, returns 0. If no pages
+ * were pinned, returns -errno.
+ */
+int get_user_pages_fast(unsigned long start, int nr_pages, int write,
+			struct page **pages)
+{
+	struct mm_struct *mm = current->mm;
+	unsigned long addr, len, end;
+	unsigned long next;
+	pgd_t *pgdp, pgd;
+	int nr = 0;
+
+	start &= PAGE_MASK;
+	addr = start;
+	len = (unsigned long) nr_pages << PAGE_SHIFT;
+	end = start + len;
+	if (end < start)
+		goto slow_irqon;
+
+	/*
+	 * local_irq_disable() doesn't prevent pagetable teardown, but does
+	 * prevent the pagetables from being freed on s390.
+	 *
+	 * So long as we atomically load page table pointers versus teardown,
+	 * we can follow the address down to the the page and take a ref on it.
+	 */
+	local_irq_disable();
+	pgdp = pgd_offset(mm, addr);
+	do {
+		pgd = *pgdp;
+		barrier();
+		next = pgd_addr_end(addr, end);
+		if (pgd_none(pgd))
+			goto slow;
+		if (!gup_pud_range(pgdp, pgd, addr, next, write, pages, &nr))
+			goto slow;
+	} while (pgdp++, addr = next, addr != end);
+	local_irq_enable();
+
+	VM_BUG_ON(nr != (end - start) >> PAGE_SHIFT);
+	return nr;
+
+	{
+		int ret;
+slow:
+		local_irq_enable();
+slow_irqon:
+		/* Try to get the remaining pages with get_user_pages */
+		start += nr << PAGE_SHIFT;
+		pages += nr;
+
+		down_read(&mm->mmap_sem);
+		ret = get_user_pages(current, mm, start,
+			(end - start) >> PAGE_SHIFT, write, 0, pages, NULL);
+		up_read(&mm->mmap_sem);
+
+		/* Have to be a bit careful with return values */
+		if (nr > 0) {
+			if (ret < 0)
+				ret = nr;
+			else
+				ret += nr;
+		}
+
+		return ret;
+	}
+}

arch/s390/mm/hugetlbpage.c

@@ -68,7 +68,7 @@ void arch_release_hugepage(struct page *page)
 	ptep = (pte_t *) page[1].index;
 	if (!ptep)
 		return;
-	pte_free(&init_mm, ptep);
+	page_table_free(&init_mm, (unsigned long *) ptep);
 	page[1].index = 0;
 }
 

arch/s390/mm/init.c

@@ -38,8 +38,6 @@
 #include <asm/tlbflush.h>
 #include <asm/sections.h>
 
-DEFINE_PER_CPU(struct mmu_gather, mmu_gathers);
-
 pgd_t swapper_pg_dir[PTRS_PER_PGD] __attribute__((__aligned__(PAGE_SIZE)));
 
 unsigned long empty_zero_page, zero_page_mask;