From mboxrd@z Thu Jan 1 00:00:00 1970 From: Catalin Marinas Subject: Re: [RFC PATCH v2 08/11] ARM64: mm: Swap PTE_FILE and PTE_PROT_NONE bits. Date: Thu, 16 May 2013 15:58:48 +0100 Message-ID: <20130516145848.GE18308@arm.com> References: <1368006763-30774-1-git-send-email-steve.capper@linaro.org> <1368006763-30774-9-git-send-email-steve.capper@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1368006763-30774-9-git-send-email-steve.capper@linaro.org> Sender: owner-linux-mm@kvack.org To: Steve Capper Cc: "linux-mm@kvack.org" , "x86@kernel.org" , "linux-arch@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Michal Hocko , Ken Chen , Mel Gorman , Will Deacon , "patches@linaro.org" List-Id: linux-arch.vger.kernel.org On Wed, May 08, 2013 at 10:52:40AM +0100, Steve Capper wrote: > Under ARM64, PTEs can be broadly categorised as follows: > - Present and valid: Bit #0 is set. The PTE is valid and memory > access to the region may fault. > > - Present and invalid: Bit #0 is clear and bit #1 is set. > Represents present memory with PROT_NONE protection. The PTE > is an invalid entry, and the user fault handler will raise a > SIGSEGV. > > - Not present (file): Bits #0 and #1 are clear, bit #2 is set. > Memory represented has been paged out. The PTE is an invalid > entry, and the fault handler will try and re-populate the > memory where necessary. > > Huge PTEs are block descriptors that have bit #1 clear. If we wish > to represent PROT_NONE huge PTEs we then run into a problem as > there is no way to distinguish between regular and huge PTEs if we > set bit #1. > > As huge PTEs are always present, the meaning of bits #1 and #2 can > be swapped for invalid PTEs. This patch swaps the PTE_FILE and > PTE_PROT_NONE constants, allowing us to represent PROT_NONE huge > PTEs. I guess we'll never get a huge_(pte|pmd)_file() (but we can shift the file bits up anyway). > Signed-off-by: Steve Capper Apart from the comments you already got: Acked-by: Catalin Marinas -- 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 fw-tnat.cambridge.arm.com ([217.140.96.21]:45801 "EHLO cam-smtp0.cambridge.arm.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751423Ab3EPPGP (ORCPT ); Thu, 16 May 2013 11:06:15 -0400 Date: Thu, 16 May 2013 15:58:48 +0100 From: Catalin Marinas Subject: Re: [RFC PATCH v2 08/11] ARM64: mm: Swap PTE_FILE and PTE_PROT_NONE bits. Message-ID: <20130516145848.GE18308@arm.com> References: <1368006763-30774-1-git-send-email-steve.capper@linaro.org> <1368006763-30774-9-git-send-email-steve.capper@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1368006763-30774-9-git-send-email-steve.capper@linaro.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Steve Capper Cc: "linux-mm@kvack.org" , "x86@kernel.org" , "linux-arch@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , Michal Hocko , Ken Chen , Mel Gorman , Will Deacon , "patches@linaro.org" Message-ID: <20130516145848.r8UHujrVHp2JvAsmOAh5mxk0JErBBRdh83pRlV4K-5g@z> On Wed, May 08, 2013 at 10:52:40AM +0100, Steve Capper wrote: > Under ARM64, PTEs can be broadly categorised as follows: > - Present and valid: Bit #0 is set. The PTE is valid and memory > access to the region may fault. > > - Present and invalid: Bit #0 is clear and bit #1 is set. > Represents present memory with PROT_NONE protection. The PTE > is an invalid entry, and the user fault handler will raise a > SIGSEGV. > > - Not present (file): Bits #0 and #1 are clear, bit #2 is set. > Memory represented has been paged out. The PTE is an invalid > entry, and the fault handler will try and re-populate the > memory where necessary. > > Huge PTEs are block descriptors that have bit #1 clear. If we wish > to represent PROT_NONE huge PTEs we then run into a problem as > there is no way to distinguish between regular and huge PTEs if we > set bit #1. > > As huge PTEs are always present, the meaning of bits #1 and #2 can > be swapped for invalid PTEs. This patch swaps the PTE_FILE and > PTE_PROT_NONE constants, allowing us to represent PROT_NONE huge > PTEs. I guess we'll never get a huge_(pte|pmd)_file() (but we can shift the file bits up anyway). > Signed-off-by: Steve Capper Apart from the comments you already got: Acked-by: Catalin Marinas