71e3aac072
Lately I've been working to make KVM use hugepages transparently without the usual restrictions of hugetlbfs. Some of the restrictions I'd like to see removed: 1) hugepages have to be swappable or the guest physical memory remains locked in RAM and can't be paged out to swap 2) if a hugepage allocation fails, regular pages should be allocated instead and mixed in the same vma without any failure and without userland noticing 3) if some task quits and more hugepages become available in the buddy, guest physical memory backed by regular pages should be relocated on hugepages automatically in regions under madvise(MADV_HUGEPAGE) (ideally event driven by waking up the kernel deamon if the order=HPAGE_PMD_SHIFT-PAGE_SHIFT list becomes not null) 4) avoidance of reservation and maximization of use of hugepages whenever possible. Reservation (needed to avoid runtime fatal faliures) may be ok for 1 machine with 1 database with 1 database cache with 1 database cache size known at boot time. It's definitely not feasible with a virtualization hypervisor usage like RHEV-H that runs an unknown number of virtual machines with an unknown size of each virtual machine with an unknown amount of pagecache that could be potentially useful in the host for guest not using O_DIRECT (aka cache=off). hugepages in the virtualization hypervisor (and also in the guest!) are much more important than in a regular host not using virtualization, becasue with NPT/EPT they decrease the tlb-miss cacheline accesses from 24 to 19 in case only the hypervisor uses transparent hugepages, and they decrease the tlb-miss cacheline accesses from 19 to 15 in case both the linux hypervisor and the linux guest both uses this patch (though the guest will limit the addition speedup to anonymous regions only for now...). Even more important is that the tlb miss handler is much slower on a NPT/EPT guest than for a regular shadow paging or no-virtualization scenario. So maximizing the amount of virtual memory cached by the TLB pays off significantly more with NPT/EPT than without (even if there would be no significant speedup in the tlb-miss runtime). The first (and more tedious) part of this work requires allowing the VM to handle anonymous hugepages mixed with regular pages transparently on regular anonymous vmas. This is what this patch tries to achieve in the least intrusive possible way. We want hugepages and hugetlb to be used in a way so that all applications can benefit without changes (as usual we leverage the KVM virtualization design: by improving the Linux VM at large, KVM gets the performance boost too). The most important design choice is: always fallback to 4k allocation if the hugepage allocation fails! This is the _very_ opposite of some large pagecache patches that failed with -EIO back then if a 64k (or similar) allocation failed... Second important decision (to reduce the impact of the feature on the existing pagetable handling code) is that at any time we can split an hugepage into 512 regular pages and it has to be done with an operation that can't fail. This way the reliability of the swapping isn't decreased (no need to allocate memory when we are short on memory to swap) and it's trivial to plug a split_huge_page* one-liner where needed without polluting the VM. Over time we can teach mprotect, mremap and friends to handle pmd_trans_huge natively without calling split_huge_page*. The fact it can't fail isn't just for swap: if split_huge_page would return -ENOMEM (instead of the current void) we'd need to rollback the mprotect from the middle of it (ideally including undoing the split_vma) which would be a big change and in the very wrong direction (it'd likely be simpler not to call split_huge_page at all and to teach mprotect and friends to handle hugepages instead of rolling them back from the middle). In short the very value of split_huge_page is that it can't fail. The collapsing and madvise(MADV_HUGEPAGE) part will remain separated and incremental and it'll just be an "harmless" addition later if this initial part is agreed upon. It also should be noted that locking-wise replacing regular pages with hugepages is going to be very easy if compared to what I'm doing below in split_huge_page, as it will only happen when page_count(page) matches page_mapcount(page) if we can take the PG_lock and mmap_sem in write mode. collapse_huge_page will be a "best effort" that (unlike split_huge_page) can fail at the minimal sign of trouble and we can try again later. collapse_huge_page will be similar to how KSM works and the madvise(MADV_HUGEPAGE) will work similar to madvise(MADV_MERGEABLE). The default I like is that transparent hugepages are used at page fault time. This can be changed with /sys/kernel/mm/transparent_hugepage/enabled. The control knob can be set to three values "always", "madvise", "never" which mean respectively that hugepages are always used, or only inside madvise(MADV_HUGEPAGE) regions, or never used. /sys/kernel/mm/transparent_hugepage/defrag instead controls if the hugepage allocation should defrag memory aggressively "always", only inside "madvise" regions, or "never". The pmd_trans_splitting/pmd_trans_huge locking is very solid. The put_page (from get_user_page users that can't use mmu notifier like O_DIRECT) that runs against a __split_huge_page_refcount instead was a pain to serialize in a way that would result always in a coherent page count for both tail and head. I think my locking solution with a compound_lock taken only after the page_first is valid and is still a PageHead should be safe but it surely needs review from SMP race point of view. In short there is no current existing way to serialize the O_DIRECT final put_page against split_huge_page_refcount so I had to invent a new one (O_DIRECT loses knowledge on the mapping status by the time gup_fast returns so...). And I didn't want to impact all gup/gup_fast users for now, maybe if we change the gup interface substantially we can avoid this locking, I admit I didn't think too much about it because changing the gup unpinning interface would be invasive. If we ignored O_DIRECT we could stick to the existing compound refcounting code, by simply adding a get_user_pages_fast_flags(foll_flags) where KVM (and any other mmu notifier user) would call it without FOLL_GET (and if FOLL_GET isn't set we'd just BUG_ON if nobody registered itself in the current task mmu notifier list yet). But O_DIRECT is fundamental for decent performance of virtualized I/O on fast storage so we can't avoid it to solve the race of put_page against split_huge_page_refcount to achieve a complete hugepage feature for KVM. Swap and oom works fine (well just like with regular pages ;). MMU notifier is handled transparently too, with the exception of the young bit on the pmd, that didn't have a range check but I think KVM will be fine because the whole point of hugepages is that EPT/NPT will also use a huge pmd when they notice gup returns pages with PageCompound set, so they won't care of a range and there's just the pmd young bit to check in that case. NOTE: in some cases if the L2 cache is small, this may slowdown and waste memory during COWs because 4M of memory are accessed in a single fault instead of 8k (the payoff is that after COW the program can run faster). So we might want to switch the copy_huge_page (and clear_huge_page too) to not temporal stores. I also extensively researched ways to avoid this cache trashing with a full prefault logic that would cow in 8k/16k/32k/64k up to 1M (I can send those patches that fully implemented prefault) but I concluded they're not worth it and they add an huge additional complexity and they remove all tlb benefits until the full hugepage has been faulted in, to save a little bit of memory and some cache during app startup, but they still don't improve substantially the cache-trashing during startup if the prefault happens in >4k chunks. One reason is that those 4k pte entries copied are still mapped on a perfectly cache-colored hugepage, so the trashing is the worst one can generate in those copies (cow of 4k page copies aren't so well colored so they trashes less, but again this results in software running faster after the page fault). Those prefault patches allowed things like a pte where post-cow pages were local 4k regular anon pages and the not-yet-cowed pte entries were pointing in the middle of some hugepage mapped read-only. If it doesn't payoff substantially with todays hardware it will payoff even less in the future with larger l2 caches, and the prefault logic would blot the VM a lot. If one is emebdded transparent_hugepage can be disabled during boot with sysfs or with the boot commandline parameter transparent_hugepage=0 (or transparent_hugepage=2 to restrict hugepages inside madvise regions) that will ensure not a single hugepage is allocated at boot time. It is simple enough to just disable transparent hugepage globally and let transparent hugepages be allocated selectively by applications in the MADV_HUGEPAGE region (both at page fault time, and if enabled with the collapse_huge_page too through the kernel daemon). This patch supports only hugepages mapped in the pmd, archs that have smaller hugepages will not fit in this patch alone. Also some archs like power have certain tlb limits that prevents mixing different page size in the same regions so they will not fit in this framework that requires "graceful fallback" to basic PAGE_SIZE in case of physical memory fragmentation. hugetlbfs remains a perfect fit for those because its software limits happen to match the hardware limits. hugetlbfs also remains a perfect fit for hugepage sizes like 1GByte that cannot be hoped to be found not fragmented after a certain system uptime and that would be very expensive to defragment with relocation, so requiring reservation. hugetlbfs is the "reservation way", the point of transparent hugepages is not to have any reservation at all and maximizing the use of cache and hugepages at all times automatically. Some performance result: vmx andrea # LD_PRELOAD=/usr/lib64/libhugetlbfs.so HUGETLB_MORECORE=yes HUGETLB_PATH=/mnt/huge/ ./largep ages3 memset page fault 1566023 memset tlb miss 453854 memset second tlb miss 453321 random access tlb miss 41635 random access second tlb miss 41658 vmx andrea # LD_PRELOAD=/usr/lib64/libhugetlbfs.so HUGETLB_MORECORE=yes HUGETLB_PATH=/mnt/huge/ ./largepages3 memset page fault 1566471 memset tlb miss 453375 memset second tlb miss 453320 random access tlb miss 41636 random access second tlb miss 41637 vmx andrea # ./largepages3 memset page fault 1566642 memset tlb miss 453417 memset second tlb miss 453313 random access tlb miss 41630 random access second tlb miss 41647 vmx andrea # ./largepages3 memset page fault 1566872 memset tlb miss 453418 memset second tlb miss 453315 random access tlb miss 41618 random access second tlb miss 41659 vmx andrea # echo 0 > /proc/sys/vm/transparent_hugepage vmx andrea # ./largepages3 memset page fault 2182476 memset tlb miss 460305 memset second tlb miss 460179 random access tlb miss 44483 random access second tlb miss 44186 vmx andrea # ./largepages3 memset page fault 2182791 memset tlb miss 460742 memset second tlb miss 459962 random access tlb miss 43981 random access second tlb miss 43988 ============ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <sys/time.h> #define SIZE (3UL*1024*1024*1024) int main() { char *p = malloc(SIZE), *p2; struct timeval before, after; gettimeofday(&before, NULL); memset(p, 0, SIZE); gettimeofday(&after, NULL); printf("memset page fault %Lu\n", (after.tv_sec-before.tv_sec)*1000000UL + after.tv_usec-before.tv_usec); gettimeofday(&before, NULL); memset(p, 0, SIZE); gettimeofday(&after, NULL); printf("memset tlb miss %Lu\n", (after.tv_sec-before.tv_sec)*1000000UL + after.tv_usec-before.tv_usec); gettimeofday(&before, NULL); memset(p, 0, SIZE); gettimeofday(&after, NULL); printf("memset second tlb miss %Lu\n", (after.tv_sec-before.tv_sec)*1000000UL + after.tv_usec-before.tv_usec); gettimeofday(&before, NULL); for (p2 = p; p2 < p+SIZE; p2 += 4096) *p2 = 0; gettimeofday(&after, NULL); printf("random access tlb miss %Lu\n", (after.tv_sec-before.tv_sec)*1000000UL + after.tv_usec-before.tv_usec); gettimeofday(&before, NULL); for (p2 = p; p2 < p+SIZE; p2 += 4096) *p2 = 0; gettimeofday(&after, NULL); printf("random access second tlb miss %Lu\n", (after.tv_sec-before.tv_sec)*1000000UL + after.tv_usec-before.tv_usec); return 0; } ============ Signed-off-by: Andrea Arcangeli <aarcange@redhat.com> Acked-by: Rik van Riel <riel@redhat.com> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
296 lines
7.2 KiB
C
296 lines
7.2 KiB
C
#ifndef _ASM_X86_PGTABLE_64_H
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#define _ASM_X86_PGTABLE_64_H
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#include <linux/const.h>
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#include <asm/pgtable_64_types.h>
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#ifndef __ASSEMBLY__
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/*
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* This file contains the functions and defines necessary to modify and use
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* the x86-64 page table tree.
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*/
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#include <asm/processor.h>
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#include <linux/bitops.h>
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#include <linux/threads.h>
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extern pud_t level3_kernel_pgt[512];
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extern pud_t level3_ident_pgt[512];
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extern pmd_t level2_kernel_pgt[512];
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extern pmd_t level2_fixmap_pgt[512];
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extern pmd_t level2_ident_pgt[512];
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extern pgd_t init_level4_pgt[];
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#define swapper_pg_dir init_level4_pgt
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extern void paging_init(void);
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#define pte_ERROR(e) \
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printk("%s:%d: bad pte %p(%016lx).\n", \
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__FILE__, __LINE__, &(e), pte_val(e))
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#define pmd_ERROR(e) \
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printk("%s:%d: bad pmd %p(%016lx).\n", \
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__FILE__, __LINE__, &(e), pmd_val(e))
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#define pud_ERROR(e) \
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printk("%s:%d: bad pud %p(%016lx).\n", \
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__FILE__, __LINE__, &(e), pud_val(e))
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#define pgd_ERROR(e) \
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printk("%s:%d: bad pgd %p(%016lx).\n", \
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__FILE__, __LINE__, &(e), pgd_val(e))
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struct mm_struct;
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void set_pte_vaddr_pud(pud_t *pud_page, unsigned long vaddr, pte_t new_pte);
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static inline void native_pte_clear(struct mm_struct *mm, unsigned long addr,
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pte_t *ptep)
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{
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*ptep = native_make_pte(0);
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}
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static inline void native_set_pte(pte_t *ptep, pte_t pte)
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{
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*ptep = pte;
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}
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static inline void native_set_pte_atomic(pte_t *ptep, pte_t pte)
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{
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native_set_pte(ptep, pte);
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}
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static inline void native_set_pmd(pmd_t *pmdp, pmd_t pmd)
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{
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*pmdp = pmd;
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}
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static inline void native_pmd_clear(pmd_t *pmd)
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{
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native_set_pmd(pmd, native_make_pmd(0));
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}
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static inline pte_t native_ptep_get_and_clear(pte_t *xp)
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{
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#ifdef CONFIG_SMP
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return native_make_pte(xchg(&xp->pte, 0));
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#else
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/* native_local_ptep_get_and_clear,
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but duplicated because of cyclic dependency */
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pte_t ret = *xp;
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native_pte_clear(NULL, 0, xp);
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return ret;
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#endif
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}
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static inline pmd_t native_pmdp_get_and_clear(pmd_t *xp)
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{
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#ifdef CONFIG_SMP
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return native_make_pmd(xchg(&xp->pmd, 0));
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#else
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/* native_local_pmdp_get_and_clear,
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but duplicated because of cyclic dependency */
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pmd_t ret = *xp;
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native_pmd_clear(xp);
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return ret;
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#endif
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}
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static inline void native_set_pud(pud_t *pudp, pud_t pud)
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{
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*pudp = pud;
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}
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static inline void native_pud_clear(pud_t *pud)
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{
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native_set_pud(pud, native_make_pud(0));
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}
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static inline void native_set_pgd(pgd_t *pgdp, pgd_t pgd)
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{
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*pgdp = pgd;
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}
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static inline void native_pgd_clear(pgd_t *pgd)
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{
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native_set_pgd(pgd, native_make_pgd(0));
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}
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extern void sync_global_pgds(unsigned long start, unsigned long end);
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/*
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* Conversion functions: convert a page and protection to a page entry,
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* and a page entry and page directory to the page they refer to.
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*/
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/*
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* Level 4 access.
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*/
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static inline int pgd_large(pgd_t pgd) { return 0; }
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#define mk_kernel_pgd(address) __pgd((address) | _KERNPG_TABLE)
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/* PUD - Level3 access */
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/* PMD - Level 2 access */
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#define pte_to_pgoff(pte) ((pte_val((pte)) & PHYSICAL_PAGE_MASK) >> PAGE_SHIFT)
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#define pgoff_to_pte(off) ((pte_t) { .pte = ((off) << PAGE_SHIFT) | \
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_PAGE_FILE })
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#define PTE_FILE_MAX_BITS __PHYSICAL_MASK_SHIFT
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/* PTE - Level 1 access. */
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/* x86-64 always has all page tables mapped. */
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#define pte_offset_map(dir, address) pte_offset_kernel((dir), (address))
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#define pte_unmap(pte) ((void)(pte))/* NOP */
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#define update_mmu_cache(vma, address, ptep) do { } while (0)
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/* Encode and de-code a swap entry */
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#if _PAGE_BIT_FILE < _PAGE_BIT_PROTNONE
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#define SWP_TYPE_BITS (_PAGE_BIT_FILE - _PAGE_BIT_PRESENT - 1)
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#define SWP_OFFSET_SHIFT (_PAGE_BIT_PROTNONE + 1)
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#else
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#define SWP_TYPE_BITS (_PAGE_BIT_PROTNONE - _PAGE_BIT_PRESENT - 1)
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#define SWP_OFFSET_SHIFT (_PAGE_BIT_FILE + 1)
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#endif
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#define MAX_SWAPFILES_CHECK() BUILD_BUG_ON(MAX_SWAPFILES_SHIFT > SWP_TYPE_BITS)
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#define __swp_type(x) (((x).val >> (_PAGE_BIT_PRESENT + 1)) \
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& ((1U << SWP_TYPE_BITS) - 1))
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#define __swp_offset(x) ((x).val >> SWP_OFFSET_SHIFT)
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#define __swp_entry(type, offset) ((swp_entry_t) { \
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((type) << (_PAGE_BIT_PRESENT + 1)) \
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| ((offset) << SWP_OFFSET_SHIFT) })
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#define __pte_to_swp_entry(pte) ((swp_entry_t) { pte_val((pte)) })
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#define __swp_entry_to_pte(x) ((pte_t) { .pte = (x).val })
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extern int kern_addr_valid(unsigned long addr);
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extern void cleanup_highmap(void);
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#define HAVE_ARCH_UNMAPPED_AREA
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#define HAVE_ARCH_UNMAPPED_AREA_TOPDOWN
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#define pgtable_cache_init() do { } while (0)
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#define check_pgt_cache() do { } while (0)
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#define PAGE_AGP PAGE_KERNEL_NOCACHE
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#define HAVE_PAGE_AGP 1
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/* fs/proc/kcore.c */
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#define kc_vaddr_to_offset(v) ((v) & __VIRTUAL_MASK)
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#define kc_offset_to_vaddr(o) ((o) | ~__VIRTUAL_MASK)
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#define __HAVE_ARCH_PTE_SAME
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#ifdef CONFIG_TRANSPARENT_HUGEPAGE
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static inline int pmd_trans_splitting(pmd_t pmd)
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{
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return pmd_val(pmd) & _PAGE_SPLITTING;
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}
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static inline int pmd_trans_huge(pmd_t pmd)
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{
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return pmd_val(pmd) & _PAGE_PSE;
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}
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#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
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#define mk_pmd(page, pgprot) pfn_pmd(page_to_pfn(page), (pgprot))
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#define __HAVE_ARCH_PMDP_SET_ACCESS_FLAGS
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extern int pmdp_set_access_flags(struct vm_area_struct *vma,
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unsigned long address, pmd_t *pmdp,
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pmd_t entry, int dirty);
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#define __HAVE_ARCH_PMDP_TEST_AND_CLEAR_YOUNG
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extern int pmdp_test_and_clear_young(struct vm_area_struct *vma,
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unsigned long addr, pmd_t *pmdp);
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#define __HAVE_ARCH_PMDP_CLEAR_YOUNG_FLUSH
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extern int pmdp_clear_flush_young(struct vm_area_struct *vma,
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unsigned long address, pmd_t *pmdp);
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#define __HAVE_ARCH_PMDP_SPLITTING_FLUSH
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extern void pmdp_splitting_flush(struct vm_area_struct *vma,
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unsigned long addr, pmd_t *pmdp);
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#define __HAVE_ARCH_PMD_WRITE
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static inline int pmd_write(pmd_t pmd)
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{
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return pmd_flags(pmd) & _PAGE_RW;
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}
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#define __HAVE_ARCH_PMDP_GET_AND_CLEAR
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static inline pmd_t pmdp_get_and_clear(struct mm_struct *mm, unsigned long addr,
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pmd_t *pmdp)
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{
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pmd_t pmd = native_pmdp_get_and_clear(pmdp);
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pmd_update(mm, addr, pmdp);
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return pmd;
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}
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#define __HAVE_ARCH_PMDP_SET_WRPROTECT
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static inline void pmdp_set_wrprotect(struct mm_struct *mm,
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unsigned long addr, pmd_t *pmdp)
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{
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clear_bit(_PAGE_BIT_RW, (unsigned long *)&pmdp->pmd);
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pmd_update(mm, addr, pmdp);
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}
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static inline int pmd_young(pmd_t pmd)
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{
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return pmd_flags(pmd) & _PAGE_ACCESSED;
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}
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static inline pmd_t pmd_set_flags(pmd_t pmd, pmdval_t set)
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{
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pmdval_t v = native_pmd_val(pmd);
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return native_make_pmd(v | set);
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}
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static inline pmd_t pmd_clear_flags(pmd_t pmd, pmdval_t clear)
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{
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pmdval_t v = native_pmd_val(pmd);
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return native_make_pmd(v & ~clear);
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}
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static inline pmd_t pmd_mkold(pmd_t pmd)
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{
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return pmd_clear_flags(pmd, _PAGE_ACCESSED);
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}
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static inline pmd_t pmd_wrprotect(pmd_t pmd)
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{
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return pmd_clear_flags(pmd, _PAGE_RW);
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}
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static inline pmd_t pmd_mkdirty(pmd_t pmd)
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{
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return pmd_set_flags(pmd, _PAGE_DIRTY);
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}
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static inline pmd_t pmd_mkhuge(pmd_t pmd)
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{
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return pmd_set_flags(pmd, _PAGE_PSE);
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}
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static inline pmd_t pmd_mkyoung(pmd_t pmd)
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{
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return pmd_set_flags(pmd, _PAGE_ACCESSED);
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}
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static inline pmd_t pmd_mkwrite(pmd_t pmd)
|
|
{
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|
return pmd_set_flags(pmd, _PAGE_RW);
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|
}
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|
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static inline pmd_t pmd_mknotpresent(pmd_t pmd)
|
|
{
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|
return pmd_clear_flags(pmd, _PAGE_PRESENT);
|
|
}
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|
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#endif /* !__ASSEMBLY__ */
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|
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#endif /* _ASM_X86_PGTABLE_64_H */
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