From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757423Ab2GLLRF (ORCPT ); Thu, 12 Jul 2012 07:17:05 -0400 Received: from cantor2.suse.de ([195.135.220.15]:56648 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754063Ab2GLLRC (ORCPT ); Thu, 12 Jul 2012 07:17:02 -0400 Date: Thu, 12 Jul 2012 13:16:59 +0200 From: Michal Hocko To: Will Deacon Cc: Hugh Dickins , Andrew Morton , Hillf Danton , "linux-arch@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" Subject: Re: [PATCH] mm: hugetlb: flush dcache before returning zeroed huge page to userspace Message-ID: <20120712111659.GF21013@tiehlicka.suse.cz> 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> <20120711174802.GG13498@mudshark.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120711174802.GG13498@mudshark.cambridge.arm.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed 11-07-12 18:48:02, Will Deacon wrote: > 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). This should go into arch specific code IMO. Even the page flag name suggests this shouldn't be in the base code. > > Will -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [PATCH] mm: hugetlb: flush dcache before returning zeroed huge page to userspace Date: Thu, 12 Jul 2012 13:16:59 +0200 Message-ID: <20120712111659.GF21013@tiehlicka.suse.cz> 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> <20120711174802.GG13498@mudshark.cambridge.arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20120711174802.GG13498@mudshark.cambridge.arm.com> Sender: owner-linux-mm@kvack.org To: Will Deacon Cc: Hugh Dickins , 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 Wed 11-07-12 18:48:02, Will Deacon wrote: > 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). This should go into arch specific code IMO. Even the page flag name suggests this shouldn't be in the base code. > > Will -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org