Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751141AbbLHSCa (ORCPT ); Tue, 8 Dec 2015 13:02:30 -0500 Received: from www.linutronix.de ([62.245.132.108]:51345 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750733AbbLHSC3 (ORCPT ); Tue, 8 Dec 2015 13:02:29 -0500 Date: Tue, 8 Dec 2015 19:01:33 +0100 (CET) From: Thomas Gleixner To: Dave Hansen cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, x86@kernel.org, dave.hansen@linux.intel.com Subject: Re: [PATCH 16/34] x86, mm: simplify get_user_pages() PTE bit handling In-Reply-To: <20151204011446.DDC6435F@viggo.jf.intel.com> Message-ID: References: <20151204011424.8A36E365@viggo.jf.intel.com> <20151204011446.DDC6435F@viggo.jf.intel.com> User-Agent: Alpine 2.11 (DEB 23 2013-08-11) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001,URIBL_BLOCKED=0.001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2777 Lines: 97 On Thu, 3 Dec 2015, Dave Hansen wrote: > > From: Dave Hansen > > The current get_user_pages() code is a wee bit more complicated > than it needs to be for pte bit checking. Currently, it establishes > a mask of required pte _PAGE_* bits and ensures that the pte it > goes after has all those bits. > > This consolidates the three identical copies of this code. > > Signed-off-by: Dave Hansen > --- > > b/arch/x86/mm/gup.c | 45 ++++++++++++++++++++++++++++----------------- > 1 file changed, 28 insertions(+), 17 deletions(-) > > diff -puN arch/x86/mm/gup.c~pkeys-16-gup-swizzle arch/x86/mm/gup.c > --- a/arch/x86/mm/gup.c~pkeys-16-gup-swizzle 2015-12-03 16:21:25.148649631 -0800 > +++ b/arch/x86/mm/gup.c 2015-12-03 16:21:25.151649767 -0800 > @@ -63,6 +63,30 @@ retry: > #endif > } > > +static inline int pte_allows_gup(pte_t pte, int write) > +{ > + /* > + * 'pte' can reall be a pte, pmd or pud. We only check > + * _PAGE_PRESENT, _PAGE_USER, and _PAGE_RW in here which > + * are the same value on all 3 types. > + */ > + if (!(pte_flags(pte) & (_PAGE_PRESENT|_PAGE_USER))) > + return 0; > + if (write && !(pte_write(pte))) > + return 0; > + return 1; > +} > + > +static inline int pmd_allows_gup(pmd_t pmd, int write) > +{ > + return pte_allows_gup(*(pte_t *)&pmd, write); > +} > + > +static inline int pud_allows_gup(pud_t pud, int write) > +{ > + return pte_allows_gup(*(pte_t *)&pud, write); > +} This still puzzles me. And the only reason it compiles is because we have -fno-strict-aliasing set ... All this operates on the pteval or even just on the pte_flags(). Even the new arch_pte_access_permitted() thingy which you add later is only interrested in pte_flags() and its just a wrapper around __pkru_allows_pkey(). So for readability and simplicity sake, can we please do something like this (pkey check already added): /* * 'pteval' can reall be a pte, pmd or pud. We only check * _PAGE_PRESENT, _PAGE_USER, and _PAGE_RW in here which * are the same value on all 3 types. */ static inline int pte_allows_gup(unsigned long pteval, int write) { unsigned long mask = _PAGE_PRESENT|_PAGE_USER; if (write) mask |= _PAGE_RW; if ((pteval & mask) != mask) return 0; if (!__pkru_allows_pkey(pte_flags_pkey(pteval), write)) return 0; return 1; } and at the callsites do: if (pte_allows_gup(pte_val(pte, write)) if (pte_allows_gup(pmd_val(pmd, write)) if (pte_allows_gup(pud_val(pud, write)) Hmm? tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/