[PATCH] Revert "x86/mm/gup: Switch GUP to the generic get_user_page_fast() implementation"

From: Ingo Molnar
Date: Sun Apr 23 2017 - 05:37:17 EST

This reverts commit 2947ba054a4dabbd82848728d765346886050029.

Dan Williams reported dax-pmem kernel warnings with the following signature:

WARNING: CPU: 8 PID: 245 at lib/percpu-refcount.c:155 percpu_ref_switch_to_atomic_rcu+0x1f5/0x200
percpu ref (dax_pmem_percpu_release [dax_pmem]) <= 0 (0) after switching to atomic

... and bisected it to this commit, which suggests possible memory corruption
caused by the x86 fast-GUP conversion.

He also pointed out:

"
This is similar to the backtrace when we were not properly handling
pud faults and was fixed with this commit: 220ced1676c4 "mm: fix
get_user_pages() vs device-dax pud mappings"

I've found some missing _devmap checks in the generic
get_user_pages_fast() path, but this does not fix the regression
[...]
"

So given that there are known bugs, and a pretty robust looking bisection
points to this commit suggesting that are unknown bugs in the conversion
as well, revert it for the time being - we'll re-try in v4.13.

Reported-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Rik van Riel <riel@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: aneesh.kumar@xxxxxxxxxxxxxxxxxx
Cc: dann.frazier@xxxxxxxxxxxxx
Cc: dave.hansen@xxxxxxxxx
Cc: steve.capper@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
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, 519 insertions(+), 128 deletions(-)

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 454fadd077ad..0d4e71b42c77 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1666,7 +1666,7 @@ config ARCH_SELECT_MEMORY_MODEL
config HAVE_ARCH_PFN_VALID
def_bool ARCH_HAS_HOLES_MEMORYMODEL || !SPARSEMEM

-config HAVE_GENERIC_GUP
+config HAVE_GENERIC_RCU_GUP
def_bool y
depends on ARM_LPAE

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index af62bf79721a..3741859765cf 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_GUP
+config HAVE_GENERIC_RCU_GUP
def_bool y

config ARCH_DMA_ADDR_T_64BIT
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 3a716b2dcde9..97a8bc8a095c 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -135,7 +135,7 @@ config PPC
select HAVE_FUNCTION_GRAPH_TRACER
select HAVE_FUNCTION_TRACER
select HAVE_GCC_PLUGINS
- select HAVE_GENERIC_GUP
+ select HAVE_GENERIC_RCU_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 a641b900fc1f..2bde14451e54 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -2789,9 +2789,6 @@ 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 6e933d2d88d9..68b329d77b3a 100644
--- a/arch/x86/include/asm/mmu_context.h
+++ b/arch/x86/include/asm/mmu_context.h
@@ -220,6 +220,18 @@ 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 c8821bab938f..50d35e3185f5 100644
--- a/arch/x86/include/asm/pgtable-3level.h
+++ b/arch/x86/include/asm/pgtable-3level.h
@@ -212,51 +212,4 @@ 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 942482ac36a8..f5af95a0c6b8 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -244,11 +244,6 @@ 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 */

@@ -1190,54 +1185,6 @@ 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 12ea31274eb6..9991224f6238 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -227,20 +227,6 @@ 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);

-#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 0fbdcb64f9f8..96d2b847e09e 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 setup_nx.o tlb.o
+ pat.o pgtable.o physaddr.o gup.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
new file mode 100644
index 000000000000..456dfdfd2249
--- /dev/null
+++ b/arch/x86/mm/gup.c
@@ -0,0 +1,496 @@
+/*
+ * 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 c89f472b658c..9b8fccb969dc 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_GUP
+config HAVE_GENERIC_RCU_GUP
bool

config ARCH_DISCARD_MEMBLOCK
diff --git a/mm/gup.c b/mm/gup.c
index 2559a3987de7..527ec2c6cca3 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -1155,7 +1155,7 @@ struct page *get_dump_page(unsigned long addr)
#endif /* CONFIG_ELF_CORE */

/*
- * Generic Fast GUP
+ * Generic RCU 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
@@ -1176,8 +1176,8 @@ struct page *get_dump_page(unsigned long addr)
* Before activating this code, please be aware that the following assumptions
* are currently made:
*
- * *) 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.
+ * *) HAVE_RCU_TABLE_FREE is enabled, and tlb_remove_table is used to free
+ * pages containing page tables.
*
* *) ptes can be read atomically by the architecture.
*
@@ -1187,7 +1187,7 @@ struct page *get_dump_page(unsigned long addr)
*
* This code is based heavily on the PowerPC implementation by Nick Piggin.
*/
-#ifdef CONFIG_HAVE_GENERIC_GUP
+#ifdef CONFIG_HAVE_GENERIC_RCU_GUP

#ifndef gup_get_pte
/*
@@ -1677,4 +1677,4 @@ int get_user_pages_fast(unsigned long start, int nr_pages, int write,
return ret;
}

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