From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [PATCHv2 1/3] x86/mm: Provide pmdp_establish() helper Date: Mon, 19 Jun 2017 16:22:29 +0100 Message-ID: <20170619152228.GE3024@e104818-lin.cambridge.arm.com> References: <20170615145224.66200-1-kirill.shutemov@linux.intel.com> <20170615145224.66200-2-kirill.shutemov@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20170615145224.66200-2-kirill.shutemov@linux.intel.com> Sender: owner-linux-mm@kvack.org To: "Kirill A. Shutemov" Cc: Andrew Morton , Vlastimil Babka , Vineet Gupta , Russell King , Will Deacon , Ralf Baechle , "David S. Miller" , "Aneesh Kumar K . V" , Martin Schwidefsky , Heiko Carstens , Andrea Arcangeli , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ingo Molnar , "H . Peter Anvin" , Thomas Gleixner List-Id: linux-arch.vger.kernel.org Hi Kirill, On Thu, Jun 15, 2017 at 05:52:22PM +0300, Kirill A. Shutemov wrote: > We need an atomic way to setup pmd page table entry, avoiding races with > CPU setting dirty/accessed bits. This is required to implement > pmdp_invalidate() that doesn't loose these bits. > > On PAE we have to use cmpxchg8b as we cannot assume what is value of new pmd and > setting it up half-by-half can expose broken corrupted entry to CPU. > > Signed-off-by: Kirill A. Shutemov > Cc: Ingo Molnar > Cc: H. Peter Anvin > Cc: Thomas Gleixner I'll look at this from the arm64 perspective. It would be good if we can have a generic atomic implementation based on cmpxchg64 but I need to look at the details first. > +static inline pmd_t pmdp_establish(pmd_t *pmdp, pmd_t pmd) > +{ > + pmd_t old; > + > + /* > + * We cannot assume what is value of pmd here, so there's no easy way > + * to set if half by half. We have to fall back to cmpxchg64. > + */ > + { BTW, you are missing a "do" here (and it probably compiles just fine without it, though different behaviour). > + old = *pmdp; > + } while (cmpxchg64(&pmdp->pmd, old.pmd, pmd.pmd) != old.pmd); > + > + return old; > +} -- Catalin -- 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.101.70]:51618 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752742AbdFSPWf (ORCPT ); Mon, 19 Jun 2017 11:22:35 -0400 Date: Mon, 19 Jun 2017 16:22:29 +0100 From: Catalin Marinas Subject: Re: [PATCHv2 1/3] x86/mm: Provide pmdp_establish() helper Message-ID: <20170619152228.GE3024@e104818-lin.cambridge.arm.com> References: <20170615145224.66200-1-kirill.shutemov@linux.intel.com> <20170615145224.66200-2-kirill.shutemov@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170615145224.66200-2-kirill.shutemov@linux.intel.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: "Kirill A. Shutemov" Cc: Andrew Morton , Vlastimil Babka , Vineet Gupta , Russell King , Will Deacon , Ralf Baechle , "David S. Miller" , "Aneesh Kumar K . V" , Martin Schwidefsky , Heiko Carstens , Andrea Arcangeli , linux-arch@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Ingo Molnar , "H . Peter Anvin" , Thomas Gleixner Message-ID: <20170619152229.pfx_fPxgXGdwuYsB32duFiaCmv-Recj2o320GsDTbw4@z> Hi Kirill, On Thu, Jun 15, 2017 at 05:52:22PM +0300, Kirill A. Shutemov wrote: > We need an atomic way to setup pmd page table entry, avoiding races with > CPU setting dirty/accessed bits. This is required to implement > pmdp_invalidate() that doesn't loose these bits. > > On PAE we have to use cmpxchg8b as we cannot assume what is value of new pmd and > setting it up half-by-half can expose broken corrupted entry to CPU. > > Signed-off-by: Kirill A. Shutemov > Cc: Ingo Molnar > Cc: H. Peter Anvin > Cc: Thomas Gleixner I'll look at this from the arm64 perspective. It would be good if we can have a generic atomic implementation based on cmpxchg64 but I need to look at the details first. > +static inline pmd_t pmdp_establish(pmd_t *pmdp, pmd_t pmd) > +{ > + pmd_t old; > + > + /* > + * We cannot assume what is value of pmd here, so there's no easy way > + * to set if half by half. We have to fall back to cmpxchg64. > + */ > + { BTW, you are missing a "do" here (and it probably compiles just fine without it, though different behaviour). > + old = *pmdp; > + } while (cmpxchg64(&pmdp->pmd, old.pmd, pmd.pmd) != old.pmd); > + > + return old; > +} -- Catalin