From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757243Ab2DFMlC (ORCPT ); Fri, 6 Apr 2012 08:41:02 -0400 Received: from mail-wg0-f44.google.com ([74.125.82.44]:51707 "EHLO mail-wg0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757140Ab2DFMlA (ORCPT ); Fri, 6 Apr 2012 08:41:00 -0400 From: Ido Yariv To: linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" Cc: Shai Fultheim , Ido Yariv Subject: [PATCH] x86: Avoid contention on cpa_lock if possible Date: Fri, 6 Apr 2012 15:40:49 +0300 Message-Id: <1333716049-26122-1-git-send-email-ido@wizery.com> X-Mailer: git-send-email 1.7.7.6 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Shai Fultheim Some architectures (e.g. vSMP) do not require to serialize cpa, for instance, by guaranteeing that the most recent TLB entry will always be used. To avoid needless contention on cpa_lock, do not lock/unlock it on such architectures. Signed-off-by: Shai Fultheim [ido@wizery.com: added should_serialize_cpa, handled potential race, and reworded the commit message] Signed-off-by: Ido Yariv --- arch/x86/mm/pageattr.c | 36 ++++++++++++++++++++++++++++-------- 1 files changed, 28 insertions(+), 8 deletions(-) diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index e1ebde3..4d606ee 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -501,7 +501,7 @@ out_unlock: return do_split; } -static int split_large_page(pte_t *kpte, unsigned long address) +static int split_large_page(pte_t *kpte, unsigned long address, bool cpa_locked) { unsigned long pfn, pfninc = 1; unsigned int i, level; @@ -509,10 +509,10 @@ static int split_large_page(pte_t *kpte, unsigned long address) pgprot_t ref_prot; struct page *base; - if (!debug_pagealloc) + if (cpa_locked) spin_unlock(&cpa_lock); base = alloc_pages(GFP_KERNEL | __GFP_NOTRACK, 0); - if (!debug_pagealloc) + if (cpa_locked) spin_lock(&cpa_lock); if (!base) return -ENOMEM; @@ -624,7 +624,8 @@ static int __cpa_process_fault(struct cpa_data *cpa, unsigned long vaddr, } } -static int __change_page_attr(struct cpa_data *cpa, int primary) +static int __change_page_attr(struct cpa_data *cpa, int primary, + bool cpa_locked) { unsigned long address; int do_split, err; @@ -693,7 +694,7 @@ repeat: /* * We have to split the large page: */ - err = split_large_page(kpte, address); + err = split_large_page(kpte, address, cpa_locked); if (!err) { /* * Do a global flush tlb after splitting the large page @@ -787,9 +788,20 @@ static int cpa_process_alias(struct cpa_data *cpa) return 0; } +static inline bool should_serialize_cpa(void) +{ + /* + * Some architectures do not require cpa() to be serialized, for + * instance, by guaranteeing that the most recent TLB entry will be + * used. + */ + return !debug_pagealloc && !is_vsmp_box(); +} + static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias) { int ret, numpages = cpa->numpages; + bool cpa_locked = false; while (numpages) { /* @@ -801,10 +813,18 @@ static int __change_page_attr_set_clr(struct cpa_data *cpa, int checkalias) if (cpa->flags & (CPA_ARRAY | CPA_PAGES_ARRAY)) cpa->numpages = 1; - if (!debug_pagealloc) + if (should_serialize_cpa()) { spin_lock(&cpa_lock); - ret = __change_page_attr(cpa, checkalias); - if (!debug_pagealloc) + /* + * In order to avoid any race conditions in which + * should_serialize_cpa() returns a different value + * after the lock was acquired, make sure locking is + * consitent and don't ever leave the lock acquired. + */ + cpa_locked = true; + } + ret = __change_page_attr(cpa, checkalias, cpa_locked); + if (cpa_locked) spin_unlock(&cpa_lock); if (ret) return ret; -- 1.7.7.6