From 465a454f254ee2ff7acc4aececbe31f8af046bc0 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Mon, 15 Jun 2009 12:31:37 +0200 Subject: x86, mm: Add __get_user_pages_fast() Introduce a gup_fast() variant which is usable from IRQ/NMI context. Signed-off-by: Peter Zijlstra CC: Nick Piggin Cc: Mike Galbraith Cc: Paul Mackerras Cc: Arnaldo Carvalho de Melo LKML-Reference: Signed-off-by: Ingo Molnar --- arch/x86/mm/gup.c | 56 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 56 insertions(+) (limited to 'arch/x86/mm') diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c index 6340cef6798..697d5727c11 100644 --- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -219,6 +219,62 @@ static int gup_pud_range(pgd_t pgd, unsigned long addr, unsigned long 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_pud_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 -- cgit v1.2.3 From 0c87197142427063e096f11603543ca874045952 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Mon, 15 Jun 2009 11:35:01 +0200 Subject: perf_counter, x86: Improve interactions with fast-gup Improve a few details in perfcounter call-chain recording that makes use of fast-GUP: - Use ACCESS_ONCE() to observe the pte value. ptes are fundamentally racy and can be changed on another CPU, so we have to be careful about how we access them. The PAE branch is already careful with read-barriers - but the non-PAE and 64-bit side needs an ACCESS_ONCE() to make sure the pte value is observed only once. - make the checks a bit stricter so that we can feed it any kind of cra^H^H^H user-space input ;-) Acked-by: Peter Zijlstra Signed-off-by: Ingo Molnar --- arch/x86/mm/gup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/mm') diff --git a/arch/x86/mm/gup.c b/arch/x86/mm/gup.c index 697d5727c11..2d1d784ad3f 100644 --- a/arch/x86/mm/gup.c +++ b/arch/x86/mm/gup.c @@ -14,7 +14,7 @@ static inline pte_t gup_get_pte(pte_t *ptep) { #ifndef CONFIG_X86_PAE - return *ptep; + return ACCESS_ONCE(*ptep); #else /* * With get_user_pages_fast, we walk down the pagetables without taking -- cgit v1.2.3