From mboxrd@z Thu Jan 1 00:00:00 1970 From: Will Deacon Subject: Re: [PATCH] mm: hugetlb: flush dcache before returning zeroed huge page to userspace Date: Wed, 11 Jul 2012 18:48:02 +0100 Message-ID: <20120711174802.GG13498@mudshark.cambridge.arm.com> References: <1341412376-6272-1-git-send-email-will.deacon@arm.com> <20120709122523.GC4627@tiehlicka.suse.cz> <20120709141324.GK7315@mudshark.cambridge.arm.com> <20120710094513.GB9108@mudshark.cambridge.arm.com> <20120710104234.GI9108@mudshark.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20120710104234.GI9108@mudshark.cambridge.arm.com> Content-Language: en-US Sender: owner-linux-mm@kvack.org To: Hugh Dickins Cc: Michal Hocko , Andrew Morton , Hillf Danton , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" List-Id: linux-arch.vger.kernel.org On Tue, Jul 10, 2012 at 11:42:34AM +0100, Will Deacon wrote: > On Tue, Jul 10, 2012 at 10:45:13AM +0100, Will Deacon wrote: > > On Tue, Jul 10, 2012 at 12:57:14AM +0100, Hugh Dickins wrote: > > > If I start to grep the architectures for non-empty flush_dcache_page(), > > > I soon find things in arch/arm such as v4_mc_copy_user_highpage() doing > > > if (!test_and_set_bit(PG_dcache_clean,)) __flush_dcache_page() - where > > > the naming suggests that I'm right, it's the architecture's responsibility > > > to arrange whatever flushing is needed in its copy and clear page functions. [...] > Ok, so this is exactly the problem. The hugetlb allocator uses its own > pool of huge pages, so free_huge_page followed by a later alloc_huge_page > will give you something where the page flags of the compound head do not > guarantee that PG_arch_1 is clear. Just to confirm, the following quick hack at least results in the correct flushing for me (on ARM): diff --git a/mm/hugetlb.c b/mm/hugetlb.c index e198831..7a7c9d3 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1141,6 +1141,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma, } set_page_private(page, (unsigned long)spool); + clear_bit(PG_arch_1, &page->flags); vma_commit_reservation(h, vma, addr); The question is whether we should tidy that up for the core code or get architectures to clear the bit in arch_make_huge_pte (which also seems to work). Will -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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Don't email: email@kvack.org From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cam-admin0.cambridge.arm.com ([217.140.96.50]:56511 "EHLO cam-admin0.cambridge.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754032Ab2GKRsN (ORCPT ); Wed, 11 Jul 2012 13:48:13 -0400 Date: Wed, 11 Jul 2012 18:48:02 +0100 From: Will Deacon Subject: Re: [PATCH] mm: hugetlb: flush dcache before returning zeroed huge page to userspace Message-ID: <20120711174802.GG13498@mudshark.cambridge.arm.com> References: <1341412376-6272-1-git-send-email-will.deacon@arm.com> <20120709122523.GC4627@tiehlicka.suse.cz> <20120709141324.GK7315@mudshark.cambridge.arm.com> <20120710094513.GB9108@mudshark.cambridge.arm.com> <20120710104234.GI9108@mudshark.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120710104234.GI9108@mudshark.cambridge.arm.com> Content-Language: en-US Sender: linux-arch-owner@vger.kernel.org List-ID: To: Hugh Dickins Cc: Michal Hocko , Andrew Morton , Hillf Danton , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" Message-ID: <20120711174802.nqk4Ggiz9jnnLH-iUOJidfMbb4vjDv6-TQG2BRx-MRU@z> On Tue, Jul 10, 2012 at 11:42:34AM +0100, Will Deacon wrote: > On Tue, Jul 10, 2012 at 10:45:13AM +0100, Will Deacon wrote: > > On Tue, Jul 10, 2012 at 12:57:14AM +0100, Hugh Dickins wrote: > > > If I start to grep the architectures for non-empty flush_dcache_page(), > > > I soon find things in arch/arm such as v4_mc_copy_user_highpage() doing > > > if (!test_and_set_bit(PG_dcache_clean,)) __flush_dcache_page() - where > > > the naming suggests that I'm right, it's the architecture's responsibility > > > to arrange whatever flushing is needed in its copy and clear page functions. [...] > Ok, so this is exactly the problem. The hugetlb allocator uses its own > pool of huge pages, so free_huge_page followed by a later alloc_huge_page > will give you something where the page flags of the compound head do not > guarantee that PG_arch_1 is clear. Just to confirm, the following quick hack at least results in the correct flushing for me (on ARM): diff --git a/mm/hugetlb.c b/mm/hugetlb.c index e198831..7a7c9d3 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -1141,6 +1141,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma, } set_page_private(page, (unsigned long)spool); + clear_bit(PG_arch_1, &page->flags); vma_commit_reservation(h, vma, addr); The question is whether we should tidy that up for the core code or get architectures to clear the bit in arch_make_huge_pte (which also seems to work). Will