[PATCHv7 01/14] x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation

Kirill A. Shutemov
2017-06-06T11:31:20Z

This patch provides all required callbacks required by the generic
get_user_pages_fast() code and switches x86 over - and removes
the platform specific implementation.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/arm/Kconfig | 2 +-
arch/arm64/Kconfig | 2 +-
arch/powerpc/Kconfig | 2 +-
arch/x86/Kconfig | 3 +
arch/x86/include/asm/mmu_context.h | 12 -
arch/x86/include/asm/pgtable-3level.h | 47 ++++
arch/x86/include/asm/pgtable.h | 53 ++++
arch/x86/include/asm/pgtable_64.h | 16 +-
arch/x86/mm/Makefile | 2 +-
arch/x86/mm/gup.c | 496 ----------------------------------
mm/Kconfig | 2 +-
mm/gup.c | 10 +-
12 files changed, 128 insertions(+), 519 deletions(-)
delete mode 100644 arch/x86/mm/gup.c

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index dabcaeb2ee3e..fce9fd34eb33 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1637,7 +1637,7 @@ config ARCH_SELECT_MEMORY_MODEL
config HAVE_ARCH_PFN_VALID
def_bool ARCH_HAS_HOLES_MEMORYMODEL || !SPARSEMEM

-config HAVE_GENERIC_RCU_GUP
+config HAVE_GENERIC_GUP
def_bool y
depends on ARM_LPAE

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 3dcd7ec69bca..a7c5f8c3f13d 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -205,7 +205,7 @@ config GENERIC_CALIBRATE_DELAY
config ZONE_DMA
def_bool y

-config HAVE_GENERIC_RCU_GUP
+config HAVE_GENERIC_GUP
def_bool y

config ARCH_DMA_ADDR_T_64BIT
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index f7c8f9972f61..7d898796c819 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -184,7 +184,7 @@ config PPC
select HAVE_FUNCTION_GRAPH_TRACER
select HAVE_FUNCTION_TRACER
select HAVE_GCC_PLUGINS
- select HAVE_GENERIC_RCU_GUP
+ select HAVE_GENERIC_GUP
select HAVE_HW_BREAKPOINT if PERF_EVENTS && (PPC_BOOK3S || PPC_8xx)
select HAVE_IDE
select HAVE_IOREMAP_PROT
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 7a065d81dc43..de71b6aca0be 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2797,6 +2797,9 @@ config X86_DMA_REMAP
bool
depends on STA2X11

+config HAVE_GENERIC_GUP
+ def_bool y
+
source "net/Kconfig"

source "drivers/Kconfig"
diff --git a/arch/x86/include/asm/mmu_context.h b/arch/x86/include/asm/mmu_context.h
index f20d7ea47095..0db8bac8b42d 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -218,18 +218,6 @@ static inline int vma_pkey(struct vm_area_struct *vma)
}
#endif

-static inline bool __pkru_allows_pkey(u16 pkey, bool write)
-{
- u32 pkru = read_pkru();
-
- if (!__pkru_allows_read(pkru, pkey))
- return false;
- if (write && !__pkru_allows_write(pkru, pkey))
- return false;
-
- return true;
-}
-
/*
* We only want to enforce protection keys on the current process
* because we effectively have no access to PKRU for other
diff --git a/arch/x86/include/asm/pgtable-3level.h b/arch/x86/include/asm/pgtable-3level.h
index 50d35e3185f5..c8821bab938f 100644
--- a/arch/x86/include/asm/pgtable-3level.h
+++ b/arch/x86/include/asm/pgtable-3level.h
@@ -212,4 +212,51 @@ static inline pud_t native_pudp_get_and_clear(pud_t *pudp)
#define __pte_to_swp_entry(pte) ((swp_entry_t){ (pte).pte_high })
#define __swp_entry_to_pte(x) ((pte_t){ { .pte_high = (x).val } })

+#define gup_get_pte gup_get_pte
+/*
+ * WARNING: only to be used in the get_user_pages_fast() implementation.
+ *
+ * With get_user_pages_fast(), we walk down the pagetables without taking
+ * any locks. For this we would like to load the pointers atomically,
+ * but that is not possible (without expensive cmpxchg8b) on PAE. What
+ * we do have is the guarantee that a PTE will only either go from not
+ * present to present, or present to not present or both -- it will not
+ * switch to a completely different present page without a TLB flush in
+ * between; something that we are blocking by holding interrupts off.
+ *
+ * Setting ptes from not present to present goes:
+ *
+ * ptep->pte_high = h;
+ * smp_wmb();
+ * ptep->pte_low = l;
+ *
+ * And present to not present goes:
+ *
+ * ptep->pte_low = 0;
+ * smp_wmb();
+ * ptep->pte_high = 0;
+ *
+ * We must ensure here that the load of pte_low sees 'l' iff pte_high
+ * sees 'h'. We load pte_high *after* loading pte_low, which ensures we
+ * don't see an older value of pte_high. *Then* we recheck pte_low,
+ * which ensures that we haven't picked up a changed pte high. We might
+ * have gotten rubbish values from pte_low and pte_high, but we are
+ * guaranteed that pte_low will not have the present bit set *unless*
+ * it is 'l'. Because get_user_pages_fast() only operates on present ptes
+ * we're safe.
+ */
+static inline pte_t gup_get_pte(pte_t *ptep)
+{
+ pte_t pte;
+
+ do {
+ pte.pte_low = ptep->pte_low;
+ smp_rmb();
+ pte.pte_high = ptep->pte_high;
+ smp_rmb();
+ } while (unlikely(pte.pte_low != ptep->pte_low));
+
+ return pte;
+}
+
#endif /* _ASM_X86_PGTABLE_3LEVEL_H */
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index f5af95a0c6b8..942482ac36a8 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -244,6 +244,11 @@ static inline int pud_devmap(pud_t pud)
return 0;
}
#endif
+
+static inline int pgd_devmap(pgd_t pgd)
+{
+ return 0;
+}
#endif
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

@@ -1185,6 +1190,54 @@ static inline u16 pte_flags_pkey(unsigned long pte_flags)
#endif
}

+static inline bool __pkru_allows_pkey(u16 pkey, bool write)
+{
+ u32 pkru = read_pkru();
+
+ if (!__pkru_allows_read(pkru, pkey))
+ return false;
+ if (write && !__pkru_allows_write(pkru, pkey))
+ return false;
+
+ return true;
+}
+
+/*
+ * 'pteval' can come from a PTE, PMD or PUD. We only check
+ * _PAGE_PRESENT, _PAGE_USER, and _PAGE_RW in here which are the
+ * same value on all 3 types.
+ */
+static inline bool __pte_access_permitted(unsigned long pteval, bool write)
+{
+ unsigned long need_pte_bits = _PAGE_PRESENT|_PAGE_USER;
+
+ if (write)
+ need_pte_bits |= _PAGE_RW;
+
+ if ((pteval & need_pte_bits) != need_pte_bits)
+ return 0;
+
+ return __pkru_allows_pkey(pte_flags_pkey(pteval), write);
+}
+
+#define pte_access_permitted pte_access_permitted
+static inline bool pte_access_permitted(pte_t pte, bool write)
+{
+ return __pte_access_permitted(pte_val(pte), write);
+}
+
+#define pmd_access_permitted pmd_access_permitted
+static inline bool pmd_access_permitted(pmd_t pmd, bool write)
+{
+ return __pte_access_permitted(pmd_val(pmd), write);
+}
+
+#define pud_access_permitted pud_access_permitted
+static inline bool pud_access_permitted(pud_t pud, bool write)
+{
+ return __pte_access_permitted(pud_val(pud), write);
+}
+
#include <asm-generic/pgtable.h>
#endif /* __ASSEMBLY__ */

diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
index 9991224f6238..12ea31274eb6 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -227,6 +227,20 @@ extern void cleanup_highmap(void);
extern void init_extra_mapping_uc(unsigned long phys, unsigned long size);
extern void init_extra_mapping_wb(unsigned long phys, unsigned long size);

-#endif /* !__ASSEMBLY__ */
+#define gup_fast_permitted gup_fast_permitted
+static inline bool gup_fast_permitted(unsigned long start, int nr_pages,
+ int write)
+{
+ unsigned long len, end;
+
+ len = (unsigned long)nr_pages << PAGE_SHIFT;
+ end = start + len;
+ if (end < start)
+ return false;
+ if (end >> __VIRTUAL_MASK_SHIFT)
+ return false;
+ return true;
+}

+#endif /* !__ASSEMBLY__ */
#endif /* _ASM_X86_PGTABLE_64_H */
diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
index 96d2b847e09e..0fbdcb64f9f8 100644
--- a/arch/x86/mm/Makefile
+++ b/arch/x86/mm/Makefile
@@ -2,7 +2,7 @@
KCOV_INSTRUMENT_tlb.o := n

obj-y := init.o init_$(BITS).o fault.o ioremap.o extable.o pageattr.o mmap.o \
- pat.o pgtable.o physaddr.o gup.o setup_nx.o tlb.o
+ pat.o pgtable.o physaddr.o setup_nx.o tlb.o

# Make sure __phys_addr has no stackprotector
nostackp := $(call cc-option, -fno-stack-protector)
diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c
deleted file mode 100644
index 456dfdfd2249..000000000000
--- a/arch/x86/mm/gup.c
+++ /dev/null
@@ -1,496 +0,0 @@
-/*
- * Lockless get_user_pages_fast for x86
- *
- * Copyright (C) 2008 Nick Piggin
- * Copyright (C) 2008 Novell Inc.
- */
-#include <linux/sched.h>
-#include <linux/mm.h>
-#include <linux/vmstat.h>
-#include <linux/highmem.h>
-#include <linux/swap.h>
-#include <linux/memremap.h>
-
-#include <asm/mmu_context.h>
-#include <asm/pgtable.h>
-
-static inline pte_t gup_get_pte(pte_t *ptep)
-{
-#ifndef CONFIG_X86_PAE
- return READ_ONCE(*ptep);
-#else
- /*
- * With get_user_pages_fast, we walk down the pagetables without taking
- * any locks. For this we would like to load the pointers atomically,
- * but that is not possible (without expensive cmpxchg8b) on PAE. What
- * we do have is the guarantee that a pte will only either go from not
- * present to present, or present to not present or both -- it will not
- * switch to a completely different present page without a TLB flush in
- * between; something that we are blocking by holding interrupts off.
- *
- * Setting ptes from not present to present goes:
- * ptep->pte_high = h;
- * smp_wmb();
- * ptep->pte_low = l;
- *
- * And present to not present goes:
- * ptep->pte_low = 0;
- * smp_wmb();
- * ptep->pte_high = 0;
- *
- * We must ensure here that the load of pte_low sees l iff pte_high
- * sees h. We load pte_high *after* loading pte_low, which ensures we
- * don't see an older value of pte_high. *Then* we recheck pte_low,
- * which ensures that we haven't picked up a changed pte high. We might
- * have got rubbish values from pte_low and pte_high, but we are
- * guaranteed that pte_low will not have the present bit set *unless*
- * it is 'l'. And get_user_pages_fast only operates on present ptes, so
- * we're safe.
- *
- * gup_get_pte should not be used or copied outside gup.c without being
- * very careful -- it does not atomically load the pte or anything that
- * is likely to be useful for you.
- */
- pte_t pte;
-
-retry:
- pte.pte_low = ptep->pte_low;
- smp_rmb();
- pte.pte_high = ptep->pte_high;
- smp_rmb();
- if (unlikely(pte.pte_low != ptep->pte_low))
- goto retry;
-
- return pte;
-#endif
-}
-
-static void undo_dev_pagemap(int *nr, int nr_start, struct page **pages)
-{
- while ((*nr) - nr_start) {
- struct page *page = pages[--(*nr)];
-
- ClearPageReferenced(page);
- put_page(page);
- }
-}
-
-/*
- * 'pteval' can come from a pte, pmd, pud or p4d. We only check
- * _PAGE_PRESENT, _PAGE_USER, and _PAGE_RW in here which are the
- * same value on all 4 types.
- */
-static inline int pte_allows_gup(unsigned long pteval, int write)
-{
- unsigned long need_pte_bits = _PAGE_PRESENT|_PAGE_USER;
-
- if (write)
- need_pte_bits |= _PAGE_RW;
-
- if ((pteval & need_pte_bits) != need_pte_bits)
- return 0;
-
- /* Check memory protection keys permissions. */
- if (!__pkru_allows_pkey(pte_flags_pkey(pteval), write))
- return 0;
-
- return 1;
-}
-
-/*
- * The performance critical leaf functions are made noinline otherwise gcc
- * inlines everything into a single function which results in too much
- * register pressure.
- */
-static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
- unsigned long end, int write, struct page **pages, int *nr)
-{
- struct dev_pagemap *pgmap = NULL;
- int nr_start = *nr, ret = 0;
- pte_t *ptep, *ptem;
-
- /*
- * Keep the original mapped PTE value (ptem) around since we
- * might increment ptep off the end of the page when finishing
- * our loop iteration.
- */
- ptem = ptep = pte_offset_map(&pmd, addr);
- do {
- pte_t pte = gup_get_pte(ptep);
- struct page *page;
-
- /* Similar to the PMD case, NUMA hinting must take slow path */
- if (pte_protnone(pte))
- break;
-
- if (!pte_allows_gup(pte_val(pte), write))
- break;
-
- if (pte_devmap(pte)) {
- pgmap = get_dev_pagemap(pte_pfn(pte), pgmap);
- if (unlikely(!pgmap)) {
- undo_dev_pagemap(nr, nr_start, pages);
- break;
- }
- } else if (pte_special(pte))
- break;
-
- VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
- page = pte_page(pte);
- get_page(page);
- put_dev_pagemap(pgmap);
- SetPageReferenced(page);
- pages[*nr] = page;
- (*nr)++;
-
- } while (ptep++, addr += PAGE_SIZE, addr != end);
- if (addr == end)
- ret = 1;
- pte_unmap(ptem);
-
- return ret;
-}
-
-static inline void get_head_page_multiple(struct page *page, int nr)
-{
- VM_BUG_ON_PAGE(page != compound_head(page), page);
- VM_BUG_ON_PAGE(page_count(page) == 0, page);
- page_ref_add(page, nr);
- SetPageReferenced(page);
-}
-
-static int __gup_device_huge(unsigned long pfn, unsigned long addr,
- unsigned long end, struct page **pages, int *nr)
-{
- int nr_start = *nr;
- struct dev_pagemap *pgmap = NULL;
-
- do {
- struct page *page = pfn_to_page(pfn);
-
- pgmap = get_dev_pagemap(pfn, pgmap);
- if (unlikely(!pgmap)) {
- undo_dev_pagemap(nr, nr_start, pages);
- return 0;
- }
- SetPageReferenced(page);
- pages[*nr] = page;
- get_page(page);
- put_dev_pagemap(pgmap);
- (*nr)++;
- pfn++;
- } while (addr += PAGE_SIZE, addr != end);
- return 1;
-}
-
-static int __gup_device_huge_pmd(pmd_t pmd, unsigned long addr,
- unsigned long end, struct page **pages, int *nr)
-{
- unsigned long fault_pfn;
-
- fault_pfn = pmd_pfn(pmd) + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
- return __gup_device_huge(fault_pfn, addr, end, pages, nr);
-}
-
-static int __gup_device_huge_pud(pud_t pud, unsigned long addr,
- unsigned long end, struct page **pages, int *nr)
-{
- unsigned long fault_pfn;
-
- fault_pfn = pud_pfn(pud) + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
- return __gup_device_huge(fault_pfn, addr, end, pages, nr);
-}
-
-static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
- unsigned long end, int write, struct page **pages, int *nr)
-{
- struct page *head, *page;
- int refs;
-
- if (!pte_allows_gup(pmd_val(pmd), write))
- return 0;
-
- VM_BUG_ON(!pfn_valid(pmd_pfn(pmd)));
- if (pmd_devmap(pmd))
- return __gup_device_huge_pmd(pmd, addr, end, pages, nr);
-
- /* hugepages are never "special" */
- VM_BUG_ON(pmd_flags(pmd) & _PAGE_SPECIAL);
-
- refs = 0;
- head = pmd_page(pmd);
- page = head + ((addr & ~PMD_MASK) >> PAGE_SHIFT);
- do {
- VM_BUG_ON_PAGE(compound_head(page) != head, page);
- pages[*nr] = page;
- (*nr)++;
- page++;
- refs++;
- } while (addr += PAGE_SIZE, addr != end);
- get_head_page_multiple(head, refs);
-
- return 1;
-}
-
-static int gup_pmd_range(pud_t pud, unsigned long addr, unsigned long end,
- int write, struct page **pages, int *nr)
-{
- unsigned long next;
- pmd_t *pmdp;
-
- pmdp = pmd_offset(&pud, addr);
- do {
- pmd_t pmd = *pmdp;
-
- next = pmd_addr_end(addr, end);
- if (pmd_none(pmd))
- return 0;
- if (unlikely(pmd_large(pmd) || !pmd_present(pmd))) {
- /*
- * NUMA hinting faults need to be handled in the GUP
- * slowpath for accounting purposes and so that they
- * can be serialised against THP migration.
- */
- if (pmd_protnone(pmd))
- return 0;
- if (!gup_huge_pmd(pmd, addr, next, write, pages, nr))
- return 0;
- } else {
- if (!gup_pte_range(pmd, addr, next, write, pages, nr))
- return 0;
- }
- } while (pmdp++, addr = next, addr != end);
-
- return 1;
-}
-
-static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
- unsigned long end, int write, struct page **pages, int *nr)
-{
- struct page *head, *page;
- int refs;
-
- if (!pte_allows_gup(pud_val(pud), write))
- return 0;
-
- VM_BUG_ON(!pfn_valid(pud_pfn(pud)));
- if (pud_devmap(pud))
- return __gup_device_huge_pud(pud, addr, end, pages, nr);
-
- /* hugepages are never "special" */
- VM_BUG_ON(pud_flags(pud) & _PAGE_SPECIAL);
-
- refs = 0;
- head = pud_page(pud);
- page = head + ((addr & ~PUD_MASK) >> PAGE_SHIFT);
- do {
- VM_BUG_ON_PAGE(compound_head(page) != head, page);
- pages[*nr] = page;
- (*nr)++;
- page++;
- refs++;
- } while (addr += PAGE_SIZE, addr != end);
- get_head_page_multiple(head, refs);
-
- return 1;
-}
-
-static int gup_pud_range(p4d_t p4d, unsigned long addr, unsigned long end,
- int write, struct page **pages, int *nr)
-{
- unsigned long next;
- pud_t *pudp;
-
- pudp = pud_offset(&p4d, addr);
- do {
- pud_t pud = *pudp;
-
- next = pud_addr_end(addr, end);
- if (pud_none(pud))
- return 0;
- if (unlikely(pud_large(pud))) {
- if (!gup_huge_pud(pud, addr, next, write, pages, nr))
- return 0;
- } else {
- if (!gup_pmd_range(pud, addr, next, write, pages, nr))
- return 0;
- }
- } while (pudp++, addr = next, addr != end);
-
- return 1;
-}
-
-static int gup_p4d_range(pgd_t pgd, unsigned long addr, unsigned long end,
- int write, struct page **pages, int *nr)
-{
- unsigned long next;
- p4d_t *p4dp;
-
- p4dp = p4d_offset(&pgd, addr);
- do {
- p4d_t p4d = *p4dp;
-
- next = p4d_addr_end(addr, end);
- if (p4d_none(p4d))
- return 0;
- BUILD_BUG_ON(p4d_large(p4d));
- if (!gup_pud_range(p4d, addr, next, write, pages, nr))
- return 0;
- } while (p4dp++, addr = next, addr != end);
-
- return 1;
-}
-
-/*
- * Like get_user_pages_fast() except its IRQ-safe in that it won't fall
- * back to the regular GUP.
- */
-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;
- unsigned long flags;
- pgd_t *pgdp;
- int nr = 0;
-
- start &= PAGE_MASK;
- addr = start;
- len = (unsigned long) nr_pages << PAGE_SHIFT;
- end = start + len;
- if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
- (void __user *)start, len)))
- return 0;
-
- /*
- * XXX: batch / limit 'nr', to avoid large irq off latency
- * needs some instrumenting to determine the common sizes used by
- * important workloads (eg. DB2), and whether limiting the batch size
- * will decrease performance.
- *
- * It seems like we're in the clear for the moment. Direct-IO is
- * the main guy that batches up lots of get_user_pages, and even
- * they are limited to 64-at-a-time which is not so many.
- */
- /*
- * This doesn't prevent pagetable teardown, but does prevent
- * the pagetables and pages from being freed on x86.
- *
- * So long as we atomically load page table pointers versus teardown
- * (which we do on x86, with the above PAE exception), we can follow the
- * address down to the the page and take a ref on it.
- */
- local_irq_save(flags);
- pgdp = pgd_offset(mm, addr);
- do {
- pgd_t pgd = *pgdp;
-
- next = pgd_addr_end(addr, end);
- if (pgd_none(pgd))
- break;
- if (!gup_p4d_range(pgd, addr, next, write, pages, &nr))
- break;
- } while (pgdp++, addr = next, addr != end);
- local_irq_restore(flags);
-
- return nr;
-}
-
-/**
- * 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;
- int nr = 0;
-
- start &= PAGE_MASK;
- addr = start;
- len = (unsigned long) nr_pages << PAGE_SHIFT;
-
- end = start + len;
- if (end < start)
- goto slow_irqon;
-
-#ifdef CONFIG_X86_64
- if (end >> __VIRTUAL_MASK_SHIFT)
- goto slow_irqon;
-#endif
-
- /*
- * XXX: batch / limit 'nr', to avoid large irq off latency
- * needs some instrumenting to determine the common sizes used by
- * important workloads (eg. DB2), and whether limiting the batch size
- * will decrease performance.
- *
- * It seems like we're in the clear for the moment. Direct-IO is
- * the main guy that batches up lots of get_user_pages, and even
- * they are limited to 64-at-a-time which is not so many.
- */
- /*
- * This doesn't prevent pagetable teardown, but does prevent
- * the pagetables and pages from being freed on x86.
- *
- * So long as we atomically load page table pointers versus teardown
- * (which we do on x86, with the above PAE exception), 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_t pgd = *pgdp;
-
- next = pgd_addr_end(addr, end);
- if (pgd_none(pgd))
- goto slow;
- if (!gup_p4d_range(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;
-
- ret = get_user_pages_unlocked(start,
- (end - start) >> PAGE_SHIFT,
- pages, write ? FOLL_WRITE : 0);
-
- /* Have to be a bit careful with return values */
- if (nr > 0) {
- if (ret < 0)
- ret = nr;
- else
- ret += nr;
- }
-
- return ret;
- }
-}
diff --git a/mm/Kconfig b/mm/Kconfig
index beb7a455915d..398b46064544 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -137,7 +137,7 @@ config HAVE_MEMBLOCK_NODE_MAP
config HAVE_MEMBLOCK_PHYS_MAP
bool

-config HAVE_GENERIC_RCU_GUP
+config HAVE_GENERIC_GUP
bool

config ARCH_DISCARD_MEMBLOCK
diff --git a/mm/gup.c b/mm/gup.c
index b3c7214d710d..2050f9fe121d 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1151,7 +1151,7 @@ struct page *get_dump_page(unsigned long addr)
#endif /* CONFIG_ELF_CORE */

/*
- * Generic RCU Fast GUP
+ * Generic Fast GUP
*
* get_user_pages_fast attempts to pin user pages by walking the page
* tables directly and avoids taking locks. Thus the walker needs to be
@@ -1172,8 +1172,8 @@ struct page *get_dump_page(unsigned long addr)
* Before activating this code, please be aware that the following assumptions
* are currently made:
*
- * *) HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table is used to free
- * pages containing page tables.
+ * *) Either HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table() is used to
+ * free pages containing page tables or TLB flushing requires IPI broadcast.
*
* *) ptes can be read atomically by the architecture.
*
@@ -1183,7 +1183,7 @@ struct page *get_dump_page(unsigned long addr)
*
* This code is based heavily on the PowerPC implementation by Nick Piggin.
*/
-#ifdef CONFIG_HAVE_GENERIC_RCU_GUP
+#ifdef CONFIG_HAVE_GENERIC_GUP

#ifndef gup_get_pte
/*
@@ -1673,4 +1673,4 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
return ret;
}

-#endif /* CONFIG_HAVE_GENERIC_RCU_GUP */
+#endif /* CONFIG_HAVE_GENERIC_GUP */
--
2.11.0

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org. For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: email@kvack.org