Recently, there was a report get_user_pages_fast helps app launching
speed due to reducing uninterruptible sleep time because we don't
need to contend for mmap_sem, I believe.
With get_user_pages_fast, that uniterruptible sleep time is reduced
about 5~10% by testing.
Cc: Russell King <li...@armlinux.org.uk>
Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Will Deacon <will.dea...@arm.com>
Cc: Steve Capper <steve.cap...@linaro.org>
Signed-off-by: Minchan Kim <minc...@kernel.org>
---
arch/arm/mm/Makefile | 6 ++
arch/arm/mm/gup.c | 221 +++++++++++++++++++++++++++++++++++++++++++
2 files changed, 227 insertions(+)
create mode 100644 arch/arm/mm/gup.c
diff --git a/arch/arm/mm/Makefile b/arch/arm/mm/Makefile
index 7cb1699fbfc4..f55f96d56843 100644
--- a/arch/arm/mm/Makefile
+++ b/arch/arm/mm/Makefile
@@ -13,6 +13,12 @@ obj-y += nommu.o
obj-$(CONFIG_ARM_MPU) += pmsa-v7.o pmsa-v8.o
endif
+ifneq ($(CONFIG_ARM_LPAE),y)
+ifeq ($(CONFIG_ARCH_HAS_PTE_SPECIAL),y)
+obj-$(CONFIG_MMU) += gup.o
+endif
+endif
+
obj-$(CONFIG_ARM_PTDUMP_CORE) += dump.o
obj-$(CONFIG_ARM_PTDUMP_DEBUGFS) += ptdump_debugfs.o
obj-$(CONFIG_MODULES) += proc-syms.o
diff --git a/arch/arm/mm/gup.c b/arch/arm/mm/gup.c
new file mode 100644
index 000000000000..4b9ce1f2d998
--- /dev/null
+++ b/arch/arm/mm/gup.c
@@ -0,0 +1,221 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/mm.h>
+#include <linux/uaccess.h>
+#include <linux/pagemap.h>
+#include <asm/pgtable.h>
+
+static inline pte_t gup_get_pte(pte_t *ptep)
+{
+ return READ_ONCE(*ptep);
+}
+
+static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
+ int write, struct page **pages, int *nr)
+{
+ int ret = 0;
+ pte_t *ptep, *ptem;
+
+ ptem = ptep = pte_offset_map(&pmd, addr);
+ do {
+ pte_t pte = gup_get_pte(ptep);
+ struct page *page;
+
+ if (!pte_access_permitted(pte, write))
+ goto pte_unmap;
+
+ if (pte_special(pte))
+ goto pte_unmap;
+
+ VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
+ page = pte_page(pte);
+
+ if (!page_cache_get_speculative(page))
+ goto pte_unmap;
+
+ if (unlikely(pte_val(pte) != pte_val(*ptep))) {
+ put_page(page);
+ goto pte_unmap;
+ }
+
+ SetPageReferenced(page);
+ pages[*nr] = page;
+ (*nr)++;
+
+ } while (ptep++, addr += PAGE_SIZE, addr != end);
+
+ ret = 1;
+
+pte_unmap:
+ pte_unmap(ptem);
+ return ret;
+}
+
+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 = READ_ONCE(*pmdp);
+
+ next = pmd_addr_end(addr, end);
+ if (!pmd_present(pmd))
+ return 0;
+ else if (!gup_pte_range(pmd, addr, next, write, pages, nr))
+ return 0;
+ } while (pmdp++, addr = next, addr != end);
+
+ return 1;
+}
+
+static int gup_pud_range(p4d_t *p4dp, unsigned long addr, unsigned long end,
+ int write, struct page **pages, int *nr)
+{
+ unsigned long next;
+ pud_t *pudp;
+
+ pudp = pud_offset(p4dp, addr);
+ do {
+ pud_t pud = READ_ONCE(*pudp);
+
+ next = pud_addr_end(addr, end);
+ if (pud_none(pud))
+ 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 *pgdp, unsigned long addr, unsigned long end,
+ int write, struct page **pages, int *nr)
+{
+ unsigned long next;
+ p4d_t *p4dp;
+
+ p4dp = p4d_offset(pgdp, addr);
+ do {
+ next = p4d_addr_end(addr, end);
+ if (p4d_none(*p4dp))
+ return 0;
+ else if (!gup_pud_range(p4dp, addr, next, write, pages, nr))
+ return 0;
+ } while (p4dp++, addr = next, addr != end);
+
+ return 1;
+}
+
+
+static void gup_pgd_range(unsigned long addr, unsigned long end,
+ int write, struct page **pages, int *nr)
+{
+ unsigned long next;
+ pgd_t *pgdp;
+
+ pgdp = pgd_offset(current->mm, addr);
+ do {
+ next = pgd_addr_end(addr, end);
+ if (pgd_none(*pgdp))
+ return;
+ else if (!gup_p4d_range(pgdp, addr, next, write, pages, nr))
+ break;
+ } while (pgdp++, addr = next, addr != end);
+}
+
+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;
+ return end >= start;
+}
+
+/*
+ * 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)
+{
+ unsigned long addr, len, end;
+ unsigned long flags;
+ 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;
+
+ /*
+ * Disable interrupts. We use the nested form as we can already have
+ * interrupts disabled by get_futex_key.
+ *
+ * With interrupts disabled, we block page table pages from being
+ * freed from under us. See mmu_gather_tlb in asm-generic/tlb.h
+ * for more details.
+ *
+ * We do not adopt an rcu_read_lock(.) here as we also want to
+ * block IPIs that come from THPs splitting.
+ */
+
+ if (gup_fast_permitted(start, nr_pages, write)) {
+ local_irq_save(flags);
+ gup_pgd_range(addr, end, write, pages, &nr);
+ local_irq_restore(flags);
+ }
+
+ return nr;
+}
+
+int get_user_pages_fast(unsigned long start, int nr_pages, int write,
+ struct page **pages)
+{
+ unsigned long addr, len, end;
+ int nr = 0, ret = 0;
+
+ start &= PAGE_MASK;
+ addr = start;
+ len = (unsigned long) nr_pages << PAGE_SHIFT;
+ end = start + len;
+
+ if (nr_pages <= 0)
+ return 0;
+
+ if (unlikely(!access_ok(write ? VERIFY_WRITE : VERIFY_READ,
+ (void __user *)start, len)))
+ return -EFAULT;
+
+ if (gup_fast_permitted(start, nr_pages, write)) {
+ local_irq_disable();
+ gup_pgd_range(addr, end, write, pages, &nr);
+ local_irq_enable();
+ ret = nr;
+ }
+
+ if (nr < nr_pages) {
+ /* Try to get the remaining pages with get_user_pages */
+ start += nr << PAGE_SHIFT;
+ pages += nr;
+
+ ret = get_user_pages_unlocked(start, nr_pages - nr, 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;
+}
--
2.19.0.397.gdd90340f6a-goog
