forked from Minki/linux
a3a9ea656d
The memory pinning code in uaccess_with_memcpy.c does not check
for HugeTLB or THP pmds, and will enter an infinite loop should
a __copy_to_user or __clear_user occur against a huge page.
This patch adds detection code for huge pages to pin_page_for_write.
As this code can be executed in a fast path it refers to the actual
pmds rather than the vma. If a HugeTLB or THP is found (they have
the same pmd representation on ARM), the page table spinlock is
taken to prevent modification whilst the page is pinned.
On ARM, huge pages are only represented as pmds, thus no huge pud
checks are performed. (For huge puds one would lock the page table
in a similar manner as in the pmd case).
Two helper functions are introduced; pmd_thp_or_huge will check
whether or not a page is huge or transparent huge (which have the
same pmd layout on ARM), and pmd_hugewillfault will detect whether
or not a page fault will occur on write to the page.
Running the following test (with the chunking from read_zero
removed):
$ dd if=/dev/zero of=/dev/null bs=10M count=1024
Gave: 2.3 GB/s backed by normal pages,
2.9 GB/s backed by huge pages,
5.1 GB/s backed by huge pages, with page mask=HPAGE_MASK.
After some discussion, it was decided not to adopt the HPAGE_MASK,
as this would have a significant detrimental effect on the overall
system latency due to page_table_lock being held for too long.
This could be revisited if split huge page locks are adopted.
Signed-off-by: Steve Capper <steve.capper@linaro.org>
Reviewed-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
194 lines
6.9 KiB
C
194 lines
6.9 KiB
C
/*
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* arch/arm/include/asm/pgtable-2level.h
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*
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* Copyright (C) 1995-2002 Russell King
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2 as
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* published by the Free Software Foundation.
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*/
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#ifndef _ASM_PGTABLE_2LEVEL_H
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#define _ASM_PGTABLE_2LEVEL_H
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/*
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* Hardware-wise, we have a two level page table structure, where the first
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* level has 4096 entries, and the second level has 256 entries. Each entry
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* is one 32-bit word. Most of the bits in the second level entry are used
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* by hardware, and there aren't any "accessed" and "dirty" bits.
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*
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* Linux on the other hand has a three level page table structure, which can
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* be wrapped to fit a two level page table structure easily - using the PGD
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* and PTE only. However, Linux also expects one "PTE" table per page, and
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* at least a "dirty" bit.
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*
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* Therefore, we tweak the implementation slightly - we tell Linux that we
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* have 2048 entries in the first level, each of which is 8 bytes (iow, two
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* hardware pointers to the second level.) The second level contains two
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* hardware PTE tables arranged contiguously, preceded by Linux versions
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* which contain the state information Linux needs. We, therefore, end up
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* with 512 entries in the "PTE" level.
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*
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* This leads to the page tables having the following layout:
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*
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* pgd pte
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* | |
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* +--------+
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* | | +------------+ +0
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* +- - - - + | Linux pt 0 |
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* | | +------------+ +1024
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* +--------+ +0 | Linux pt 1 |
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* | |-----> +------------+ +2048
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* +- - - - + +4 | h/w pt 0 |
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* | |-----> +------------+ +3072
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* +--------+ +8 | h/w pt 1 |
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* | | +------------+ +4096
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*
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* See L_PTE_xxx below for definitions of bits in the "Linux pt", and
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* PTE_xxx for definitions of bits appearing in the "h/w pt".
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*
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* PMD_xxx definitions refer to bits in the first level page table.
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*
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* The "dirty" bit is emulated by only granting hardware write permission
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* iff the page is marked "writable" and "dirty" in the Linux PTE. This
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* means that a write to a clean page will cause a permission fault, and
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* the Linux MM layer will mark the page dirty via handle_pte_fault().
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* For the hardware to notice the permission change, the TLB entry must
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* be flushed, and ptep_set_access_flags() does that for us.
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*
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* The "accessed" or "young" bit is emulated by a similar method; we only
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* allow accesses to the page if the "young" bit is set. Accesses to the
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* page will cause a fault, and handle_pte_fault() will set the young bit
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* for us as long as the page is marked present in the corresponding Linux
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* PTE entry. Again, ptep_set_access_flags() will ensure that the TLB is
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* up to date.
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*
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* However, when the "young" bit is cleared, we deny access to the page
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* by clearing the hardware PTE. Currently Linux does not flush the TLB
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* for us in this case, which means the TLB will retain the transation
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* until either the TLB entry is evicted under pressure, or a context
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* switch which changes the user space mapping occurs.
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*/
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#define PTRS_PER_PTE 512
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#define PTRS_PER_PMD 1
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#define PTRS_PER_PGD 2048
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#define PTE_HWTABLE_PTRS (PTRS_PER_PTE)
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#define PTE_HWTABLE_OFF (PTE_HWTABLE_PTRS * sizeof(pte_t))
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#define PTE_HWTABLE_SIZE (PTRS_PER_PTE * sizeof(u32))
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/*
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* PMD_SHIFT determines the size of the area a second-level page table can map
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* PGDIR_SHIFT determines what a third-level page table entry can map
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*/
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#define PMD_SHIFT 21
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#define PGDIR_SHIFT 21
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#define PMD_SIZE (1UL << PMD_SHIFT)
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#define PMD_MASK (~(PMD_SIZE-1))
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#define PGDIR_SIZE (1UL << PGDIR_SHIFT)
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#define PGDIR_MASK (~(PGDIR_SIZE-1))
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/*
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* section address mask and size definitions.
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*/
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#define SECTION_SHIFT 20
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#define SECTION_SIZE (1UL << SECTION_SHIFT)
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#define SECTION_MASK (~(SECTION_SIZE-1))
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/*
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* ARMv6 supersection address mask and size definitions.
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*/
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#define SUPERSECTION_SHIFT 24
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#define SUPERSECTION_SIZE (1UL << SUPERSECTION_SHIFT)
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#define SUPERSECTION_MASK (~(SUPERSECTION_SIZE-1))
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#define USER_PTRS_PER_PGD (TASK_SIZE / PGDIR_SIZE)
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/*
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* "Linux" PTE definitions.
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*
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* We keep two sets of PTEs - the hardware and the linux version.
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* This allows greater flexibility in the way we map the Linux bits
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* onto the hardware tables, and allows us to have YOUNG and DIRTY
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* bits.
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*
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* The PTE table pointer refers to the hardware entries; the "Linux"
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* entries are stored 1024 bytes below.
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*/
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#define L_PTE_VALID (_AT(pteval_t, 1) << 0) /* Valid */
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#define L_PTE_PRESENT (_AT(pteval_t, 1) << 0)
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#define L_PTE_YOUNG (_AT(pteval_t, 1) << 1)
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#define L_PTE_FILE (_AT(pteval_t, 1) << 2) /* only when !PRESENT */
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#define L_PTE_DIRTY (_AT(pteval_t, 1) << 6)
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#define L_PTE_RDONLY (_AT(pteval_t, 1) << 7)
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#define L_PTE_USER (_AT(pteval_t, 1) << 8)
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#define L_PTE_XN (_AT(pteval_t, 1) << 9)
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#define L_PTE_SHARED (_AT(pteval_t, 1) << 10) /* shared(v6), coherent(xsc3) */
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#define L_PTE_NONE (_AT(pteval_t, 1) << 11)
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/*
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* These are the memory types, defined to be compatible with
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* pre-ARMv6 CPUs cacheable and bufferable bits: XXCB
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*/
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#define L_PTE_MT_UNCACHED (_AT(pteval_t, 0x00) << 2) /* 0000 */
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#define L_PTE_MT_BUFFERABLE (_AT(pteval_t, 0x01) << 2) /* 0001 */
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#define L_PTE_MT_WRITETHROUGH (_AT(pteval_t, 0x02) << 2) /* 0010 */
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#define L_PTE_MT_WRITEBACK (_AT(pteval_t, 0x03) << 2) /* 0011 */
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#define L_PTE_MT_MINICACHE (_AT(pteval_t, 0x06) << 2) /* 0110 (sa1100, xscale) */
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#define L_PTE_MT_WRITEALLOC (_AT(pteval_t, 0x07) << 2) /* 0111 */
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#define L_PTE_MT_DEV_SHARED (_AT(pteval_t, 0x04) << 2) /* 0100 */
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#define L_PTE_MT_DEV_NONSHARED (_AT(pteval_t, 0x0c) << 2) /* 1100 */
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#define L_PTE_MT_DEV_WC (_AT(pteval_t, 0x09) << 2) /* 1001 */
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#define L_PTE_MT_DEV_CACHED (_AT(pteval_t, 0x0b) << 2) /* 1011 */
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#define L_PTE_MT_MASK (_AT(pteval_t, 0x0f) << 2)
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#ifndef __ASSEMBLY__
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/*
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* The "pud_xxx()" functions here are trivial when the pmd is folded into
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* the pud: the pud entry is never bad, always exists, and can't be set or
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* cleared.
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*/
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#define pud_none(pud) (0)
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#define pud_bad(pud) (0)
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#define pud_present(pud) (1)
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#define pud_clear(pudp) do { } while (0)
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#define set_pud(pud,pudp) do { } while (0)
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static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
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{
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return (pmd_t *)pud;
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}
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#define pmd_bad(pmd) (pmd_val(pmd) & 2)
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#define copy_pmd(pmdpd,pmdps) \
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do { \
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pmdpd[0] = pmdps[0]; \
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pmdpd[1] = pmdps[1]; \
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flush_pmd_entry(pmdpd); \
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} while (0)
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#define pmd_clear(pmdp) \
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do { \
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pmdp[0] = __pmd(0); \
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pmdp[1] = __pmd(0); \
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clean_pmd_entry(pmdp); \
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} while (0)
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/* we don't need complex calculations here as the pmd is folded into the pgd */
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#define pmd_addr_end(addr,end) (end)
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#define set_pte_ext(ptep,pte,ext) cpu_set_pte_ext(ptep,pte,ext)
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/*
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* We don't have huge page support for short descriptors, for the moment
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* define empty stubs for use by pin_page_for_write.
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*/
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#define pmd_hugewillfault(pmd) (0)
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#define pmd_thp_or_huge(pmd) (0)
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#endif /* __ASSEMBLY__ */
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#endif /* _ASM_PGTABLE_2LEVEL_H */
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