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[2607:7c80:54:e::133]) by mx.google.com with ESMTPS id p9-v6si3880230pgi.553.2018.09.13.02.29.45 for (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 13 Sep 2018 02:29:45 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of peterz@infradead.org designates 2607:7c80:54:e::133 as permitted sender) client-ip=2607:7c80:54:e::133; Authentication-Results: mx.google.com; dkim=pass header.i=@infradead.org header.s=bombadil.20170209 header.b=WZwLYVgX; spf=pass (google.com: best guess record for domain of peterz@infradead.org designates 2607:7c80:54:e::133 as permitted sender) smtp.mailfrom=peterz@infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Content-Type:MIME-Version:References: Subject:Cc:To:From:Date:Message-ID:Sender:Reply-To:Content-Transfer-Encoding: Content-ID:Content-Description:Resent-Date:Resent-From:Resent-Sender: Resent-To:Resent-Cc:Resent-Message-ID:In-Reply-To:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Bdpi8XYGmctjDZDpmcUjIYicrWhlqIYbn1DDQ6wv/28=; b=WZwLYVgXbE4QAVC6YGSbu6zs7H Gfe7C5NXtHM1il+Nq8mtrPXRRTUgcSCde8VCMVlm/PSVXXjDZ/dBvPp/Uxmr+QwZ5tg2LCHrtGucl xHUrgzP95PGdKZPq3AqbOcb3ovOh/yHYRkoBYKG8zlHmVJTtnPW8ToGZhJHFPXRpMX1IWsf6tVCm1 hxJQlgruft8fdmaIrOqIXtbNyyiXrS4rSMJT/O535VWeLTEf2sCHp9Nrw/Ipw65yvZOXKLfrHGvnu peVWzu2+7L+5nWAcsbsJ//nIQMw21TpsxN0invyjx8/dxZJlPvc2n8plj8F2fgTojvpFSAKMzzzPc pfI8kSbA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1g0Nw0-0000ur-GV; Thu, 13 Sep 2018 09:29:12 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 0) id 3B63920147C5D; Thu, 13 Sep 2018 11:29:10 +0200 (CEST) Message-ID: <20180913092811.894806629@infradead.org> User-Agent: quilt/0.65 Date: Thu, 13 Sep 2018 11:21:11 +0200 From: Peter Zijlstra To: will.deacon@arm.com, aneesh.kumar@linux.vnet.ibm.com, akpm@linux-foundation.org, npiggin@gmail.com Cc: linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, peterz@infradead.org, linux@armlinux.org.uk, heiko.carstens@de.ibm.com Subject: [RFC][PATCH 01/11] asm-generic/tlb: Provide a comment References: <20180913092110.817204997@infradead.org> MIME-Version: 1.0 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: X-Virus-Scanned: ClamAV using ClamSMTP Write a comment explaining some of this.. Cc: Will Deacon Cc: "Aneesh Kumar K.V" Cc: Andrew Morton Cc: Nick Piggin Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Martin Schwidefsky --- include/asm-generic/tlb.h | 120 ++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 117 insertions(+), 3 deletions(-) --- a/include/asm-generic/tlb.h +++ b/include/asm-generic/tlb.h @@ -22,6 +22,119 @@ #ifdef CONFIG_MMU +/* + * Generic MMU-gather implementation. + * + * The mmu_gather data structure is used by the mm code to implement the + * correct and efficient ordering of freeing pages and TLB invalidations. + * + * This correct ordering is: + * + * 1) unhook page + * 2) TLB invalidate page + * 3) free page + * + * That is, we must never free a page before we have ensured there are no live + * translations left to it. Otherwise it might be possible to observe (or + * worse, change) the page content after it has been reused. + * + * The mmu_gather API consists of: + * + * - tlb_gather_mmu() / tlb_finish_mmu(); start and finish a mmu_gather + * + * Finish in particular will issue a (final) TLB invalidate and free + * all (remaining) queued pages. + * + * - tlb_start_vma() / tlb_end_vma(); marks the start / end of a VMA + * + * Defaults to flushing at tlb_end_vma() to reset the range; helps when + * there's large holes between the VMAs. + * + * - tlb_remove_page() / __tlb_remove_page() + * - tlb_remove_page_size() / __tlb_remove_page_size() + * + * __tlb_remove_page_size() is the basic primitive that queues a page for + * freeing. __tlb_remove_page() assumes PAGE_SIZE. Both will return a + * boolean indicating if the queue is (now) full and a call to + * tlb_flush_mmu() is required. + * + * tlb_remove_page() and tlb_remove_page_size() imply the call to + * tlb_flush_mmu() when required and has no return value. + * + * - tlb_change_page_size() + * + * call before __tlb_remove_page*() to set the current page-size; implies a + * possible tlb_flush_mmu() call. + * + * - tlb_flush_mmu() / tlb_flush_mmu_tlbonly() / tlb_flush_mmu_free() + * + * tlb_flush_mmu_tlbonly() - does the TLB invalidate (and resets + * related state, like the range) + * + * tlb_flush_mmu_free() - frees the queued pages; make absolutely + * sure no additional tlb_remove_page() + * calls happen between _tlbonly() and this. + * + * tlb_flush_mmu() - the above two calls. + * + * - mmu_gather::fullmm + * + * A flag set by tlb_gather_mmu() to indicate we're going to free + * the entire mm; this allows a number of optimizations. + * + * XXX list optimizations + * + * - mmu_gather::need_flush_all + * + * A flag that can be set by the arch code if it wants to force + * flush the entire TLB irrespective of the range. For instance + * x86-PAE needs this when changing top-level entries. + * + * And requires the architecture to provide and implement tlb_flush(). + * + * tlb_flush() may, in addition to the above mentioned mmu_gather fields, make + * use of: + * + * - mmu_gather::start / mmu_gather::end + * + * which (when !need_flush_all; fullmm will have start = end = ~0UL) provides + * the range that needs to be flushed to cover the pages to be freed. + * + * - mmu_gather::freed_tables + * + * set when we freed page table pages + * + * - tlb_get_unmap_shift() / tlb_get_unmap_size() + * + * returns the smallest TLB entry size unmapped in this range + * + * Additionally there are a few opt-in features: + * + * HAVE_MMU_GATHER_PAGE_SIZE + * + * This ensures we call tlb_flush() every time tlb_change_page_size() actually + * changes the size and provides mmu_gather::page_size to tlb_flush(). + * + * HAVE_RCU_TABLE_FREE + * + * This provides tlb_remove_table(), to be used instead of tlb_remove_page() + * for page directores (__p*_free_tlb()). This provides separate freeing of + * the page-table pages themselves in a semi-RCU fashion (see comment below). + * Useful if your architecture doesn't use IPIs for remote TLB invalidates + * and therefore doesn't naturally serialize with software page-table walkers. + * + * When used, an architecture is expected to provide __tlb_remove_table() + * which does the actual freeing of these pages. + * + * HAVE_RCU_TABLE_INVALIDATE + * + * This makes HAVE_RCU_TABLE_FREE call tlb_flush_mmu_tlbonly() before freeing + * the page-table pages. Required if you use HAVE_RCU_TABLE_FREE and your + * architecture uses the Linux page-tables natively. + * + */ +#define HAVE_GENERIC_MMU_GATHER + #ifdef CONFIG_HAVE_RCU_TABLE_FREE /* * Semi RCU freeing of the page directories. @@ -89,14 +202,17 @@ struct mmu_gather_batch { */ #define MAX_GATHER_BATCH_COUNT (10000UL/MAX_GATHER_BATCH) -/* struct mmu_gather is an opaque type used by the mm code for passing around +/* + * struct mmu_gather is an opaque type used by the mm code for passing around * any data needed by arch specific code for tlb_remove_page. */ struct mmu_gather { struct mm_struct *mm; + #ifdef CONFIG_HAVE_RCU_TABLE_FREE struct mmu_table_batch *batch; #endif + unsigned long start; unsigned long end; /* @@ -131,8 +247,6 @@ struct mmu_gather { int page_size; }; -#define HAVE_GENERIC_MMU_GATHER - void arch_tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm, unsigned long start, unsigned long end); void tlb_flush_mmu(struct mmu_gather *tlb);