From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756854AbaEPJwP (ORCPT ); Fri, 16 May 2014 05:52:15 -0400 Received: from fw-tnat.austin.arm.com ([217.140.110.23]:50014 "EHLO collaborate-mta1.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751475AbaEPJwM (ORCPT ); Fri, 16 May 2014 05:52:12 -0400 Date: Fri, 16 May 2014 10:51:25 +0100 From: Catalin Marinas To: "msalter@redhat.com" Cc: Steve Capper , Will Deacon , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH] arm64: fix pud_huge() for 2-level pagetables Message-ID: <20140516095125.GF5624@arm.com> References: <1400163562-7481-1-git-send-email-msalter@redhat.com> <20140515144424.GA23884@linaro.org> <1400171258.21547.136.camel@deneb.redhat.com> <1400179157.21547.147.camel@deneb.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1400179157.21547.147.camel@deneb.redhat.com> Thread-Topic: [PATCH] arm64: fix pud_huge() for 2-level pagetables Accept-Language: en-GB, en-US Content-Language: en-US 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 Thu, May 15, 2014 at 07:39:17PM +0100, Mark Salter wrote: > On Thu, 2014-05-15 at 18:55 +0100, Steve Capper wrote: > > On 15 May 2014 17:27, Mark Salter wrote: > > > On Thu, 2014-05-15 at 15:44 +0100, Steve Capper wrote: > > >> On Thu, May 15, 2014 at 10:19:22AM -0400, Mark Salter wrote: > > >> > In arch/arm/kvm/mmu.c:unmap_range(), we end up doing an extra put_page() > > >> > on the stage2 pgd which leads to the BUG in put_page_testzero(). This > > >> > happens because a pud_huge() test in unmap_range() returns true when it > > >> > should always be false with 2-level pages tables used by 64k pages. > > >> > This patch removes support for huge puds if 2-level pagetables are > > >> > being used. [...] > > Yeah I agree for 64K granule it doesn't make sense to have a huge_pud. > > The patch looks sound now, but checking for a folded pmd may run into > > problems if/when we get to 3-levels and 64K pages in future. > > > > Perhaps checking for PAGE_SHIFT==12 (or something similar) would be a > > bit more robust? > > I don't think testing based on granule size is generally correct either. > Maybe support for 3-level page tables with 64k granule gets added as an > option. That would break the pagesize based test. With a folded pmd, we > know there is no pud, so pud_huge() should always be false. I agree, pud_huge() should be false in the same way we define pud_present() to be 1 when __PGTABLE_PMD_FOLDED. The *_huge() macros aren't covered by the generic headers unfortunately (some clean-up would be useful at some point but for now this patch is fine). -- Catalin