Messages in this thread Patch in this message |  | | From | Bin Yang <> | Subject | [PATCH v3 2/5] x86/mm: avoid static_protection() checking if not whole large page attr change | Date | Tue, 21 Aug 2018 01:16:23 +0000 |
| |
The range check whether the address is aligned to the large page and covers the full large page (1G or 2M) is obvious to do _before_ static_protection() check, because if the requested range does not fit and has a different pgprot_val() then it will decide to split after the check anyway.
The approach and some of the comments came from Thomas Gleixner's email example for how to do this
Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Bin Yang <bin.yang@intel.com> --- arch/x86/mm/pageattr.c | 35 ++++++++++++++++------------------- 1 file changed, 16 insertions(+), 19 deletions(-)
diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index 68613fd..091f1d3 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -645,11 +645,21 @@ try_preserve_large_page(pte_t *kpte, unsigned long address, } /* + * If the requested address range is not aligned to the start of + * the large page or does not cover the full range, split it up. + * No matter what the static_protections() check below does, it + * would anyway result in a split after doing all the check work + * for nothing. + */ + addr = address & pmask; + if (address != addr || cpa->numpages != numpages) + goto out_unlock; + + /* * We need to check the full range, whether * static_protection() requires a different pgprot for one of * the pages in the range we try to preserve: */ - addr = address & pmask; pfn = old_pfn; for (i = 0; i < (psize >> PAGE_SHIFT); i++, addr += PAGE_SIZE, pfn++) { pgprot_t chk_prot = static_protections(req_prot, addr, pfn); @@ -659,24 +669,11 @@ try_preserve_large_page(pte_t *kpte, unsigned long address, } - /* - * 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 == (address & pmask) && cpa->numpages == (psize >> PAGE_SHIFT)) { - /* - * The address is aligned and the number of pages - * covers the full page. - */ - new_pte = pfn_pte(old_pfn, new_prot); - __set_pmd_pte(kpte, address, new_pte); - cpa->flags |= CPA_FLUSHTLB; - do_split = 0; - } + /* All checks passed. Just change the large mapping entry */ + new_pte = pfn_pte(old_pfn, new_prot); + __set_pmd_pte(kpte, address, new_pte); + cpa->flags |= CPA_FLUSHTLB; + do_split = 0; out_unlock: spin_unlock(&pgd_lock); -- 2.7.4
|  |