From 65e074dffa198978ab0c9976a19b954fbe1183e2 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Mon, 4 Feb 2008 16:48:07 +0100 Subject: x86: cpa, preserve large pages if possible When CPA is called on a range which fits into a large page mapping, avoid to split the page when: 1) There is no change of attributes 2) The range to change is a complete large mapping Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar --- arch/x86/mm/pageattr.c | 142 ++++++++++++++++++++++++++++++++++++++++++++----- 1 file changed, 130 insertions(+), 12 deletions(-) (limited to 'arch/x86/mm/pageattr.c') diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index 79a9f1b42ddd..40b7ac58e671 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -18,12 +18,17 @@ struct cpa_data { unsigned long vaddr; - int numpages; pgprot_t mask_set; pgprot_t mask_clr; + int numpages; int flushtlb; }; +enum { + CPA_NO_SPLIT = 0, + CPA_SPLIT, +}; + static inline int within(unsigned long addr, unsigned long start, unsigned long end) { @@ -230,6 +235,86 @@ static void __set_pmd_pte(pte_t *kpte, unsigned long address, pte_t pte) #endif } +static int try_preserve_large_page(pte_t *kpte, unsigned long address, + struct cpa_data *cpa) +{ + unsigned long nextpage_addr, numpages, pmask, psize, flags; + pte_t new_pte, old_pte, *tmp; + pgprot_t old_prot, new_prot; + int level, res = CPA_SPLIT; + + spin_lock_irqsave(&pgd_lock, flags); + /* + * Check for races, another CPU might have split this page + * up already: + */ + tmp = lookup_address(address, &level); + if (tmp != kpte) + goto out_unlock; + + switch (level) { + case PG_LEVEL_2M: + psize = LARGE_PAGE_SIZE; + pmask = LARGE_PAGE_MASK; + break; + case PG_LEVEL_1G: + default: + res = -EINVAL; + goto out_unlock; + } + + /* + * Calculate the number of pages, which fit into this large + * page starting at address: + */ + nextpage_addr = (address + psize) & pmask; + numpages = (nextpage_addr - address) >> PAGE_SHIFT; + if (numpages < cpa->numpages) + cpa->numpages = numpages; + + /* + * We are safe now. Check whether the new pgprot is the same: + */ + old_pte = *kpte; + old_prot = new_prot = pte_pgprot(old_pte); + + pgprot_val(new_prot) &= ~pgprot_val(cpa->mask_clr); + pgprot_val(new_prot) |= pgprot_val(cpa->mask_set); + new_prot = static_protections(new_prot, address); + + /* + * If there are no changes, return. maxpages has been updated + * above: + */ + if (pgprot_val(new_prot) == pgprot_val(old_prot)) { + res = CPA_NO_SPLIT; + goto out_unlock; + } + + /* + * We need to change the attributes. Check, whether we can + * change the large page in one go. We request a split, when + * the address is not aligned and the number of pages is + * smaller than the number of pages in the large page. Note + * that we limited the number of possible pages already to + * the number of pages in the large page. + */ + if (address == (nextpage_addr - psize) && cpa->numpages == numpages) { + /* + * The address is aligned and the number of pages + * covers the full page. + */ + new_pte = pfn_pte(pte_pfn(old_pte), canon_pgprot(new_prot)); + __set_pmd_pte(kpte, address, new_pte); + cpa->flushtlb = 1; + res = CPA_NO_SPLIT; + } + +out_unlock: + spin_unlock_irqrestore(&pgd_lock, flags); + return res; +} + static int split_large_page(pte_t *kpte, unsigned long address) { pgprot_t ref_prot = pte_pgprot(pte_clrhuge(*kpte)); @@ -295,7 +380,7 @@ out_unlock: static int __change_page_attr(unsigned long address, struct cpa_data *cpa) { struct page *kpte_page; - int level, err = 0; + int level, res; pte_t *kpte; repeat: @@ -338,13 +423,34 @@ repeat: set_pte_atomic(kpte, new_pte); cpa->flushtlb = 1; } - } else { - err = split_large_page(kpte, address); - if (!err) - goto repeat; - cpa->flushtlb = 1; + cpa->numpages = 1; + return 0; } - return err; + + /* + * Check, whether we can keep the large page intact + * and just change the pte: + */ + res = try_preserve_large_page(kpte, address, cpa); + if (res < 0) + return res; + + /* + * When the range fits into the existing large page, + * return. cp->numpages and cpa->tlbflush have been updated in + * try_large_page: + */ + if (res == CPA_NO_SPLIT) + return 0; + + /* + * We have to split the large page: + */ + res = split_large_page(kpte, address); + if (res) + return res; + cpa->flushtlb = 1; + goto repeat; } /** @@ -410,15 +516,27 @@ static int change_page_attr_addr(struct cpa_data *cpa) static int __change_page_attr_set_clr(struct cpa_data *cpa) { - unsigned int i; - int ret; + int ret, numpages = cpa->numpages; - for (i = 0; i < cpa->numpages ; i++, cpa->vaddr += PAGE_SIZE) { + while (numpages) { + /* + * Store the remaining nr of pages for the large page + * preservation check. + */ + cpa->numpages = numpages; ret = change_page_attr_addr(cpa); if (ret) return ret; - } + /* + * Adjust the number of pages with the result of the + * CPA operation. Either a large page has been + * preserved or a single page update happened. + */ + BUG_ON(cpa->numpages > numpages); + numpages -= cpa->numpages; + cpa->vaddr += cpa->numpages * PAGE_SIZE; + } return 0; } -- cgit v1.2.3-55-g7522