From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966430Ab2C3Vpb (ORCPT ); Fri, 30 Mar 2012 17:45:31 -0400 Received: from acsinet15.oracle.com ([141.146.126.227]:35478 "EHLO acsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S966096Ab2C3VpZ (ORCPT ); Fri, 30 Mar 2012 17:45:25 -0400 Date: Fri, 30 Mar 2012 17:40:05 -0400 From: Konrad Rzeszutek Wilk To: Andrea Arcangeli Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Hillf Danton , Dan Smith , Peter Zijlstra , Linus Torvalds , Andrew Morton , Thomas Gleixner , Ingo Molnar , Paul Turner , Suresh Siddha , Mike Galbraith , "Paul E. McKenney" , Lai Jiangshan , Bharata B Rao , Lee Schermerhorn , Rik van Riel , Johannes Weiner Subject: Re: [PATCH 02/39] xen: document Xen is using an unused bit for the pagetables Message-ID: <20120330214005.GC23599@phenom.dumpdata.com> References: <1332783986-24195-1-git-send-email-aarcange@redhat.com> <1332783986-24195-3-git-send-email-aarcange@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1332783986-24195-3-git-send-email-aarcange@redhat.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: ucsinet22.oracle.com [156.151.31.94] X-CT-RefId: str=0001.0A090202.4F76294C.0097,ss=1,re=0.000,fgs=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 26, 2012 at 07:45:49PM +0200, Andrea Arcangeli wrote: > Xen has taken over the last reserved bit available for the pagetables > which is set through ioremap, this documents it and makes the code > more readable. About a year ago we redid the P2M code to ditch the major use case for this. But there were two left over cases that I hadn't found a good solution for that would allow us to completly eliminate the use of this bit: 1). When setting a PTE of a PFN which overlaps an E820 hole or any of the non-E820-RAM entries, we lookup in the P2M and find out that the PFN is a 1:1 and return a pte.pte | pfn << PAGE_SIZE. But we also stick the _PAGE_IOMAP on it so that when the call to xen_pte_val is done we don't end up doing the lookup in the P2M tree once more and just set the pte as is. So this is the dance between xen_pte_val and xen_make_pte. 2). When the userspace tries to mmap a guest memory for save/migrate or to setup something in the guest, it would use the xen_remap_domain_mfn_range to setup PTE's with the guest's PFN (gpfn). The _PAGE_IOMAP is used again to tell xen_pte_val to not bother looking it up in the P2M tree and use it as is. So.. any thoughts on how to eliminate the usage of this? > > Signed-off-by: Andrea Arcangeli > --- > arch/x86/include/asm/pgtable_types.h | 11 +++++++++-- > 1 files changed, 9 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h > index 013286a..b74cac9 100644 > --- a/arch/x86/include/asm/pgtable_types.h > +++ b/arch/x86/include/asm/pgtable_types.h > @@ -17,7 +17,7 @@ > #define _PAGE_BIT_PAT 7 /* on 4KB pages */ > #define _PAGE_BIT_GLOBAL 8 /* Global TLB entry PPro+ */ > #define _PAGE_BIT_UNUSED1 9 /* available for programmer */ > -#define _PAGE_BIT_IOMAP 10 /* flag used to indicate IO mapping */ > +#define _PAGE_BIT_UNUSED2 10 > #define _PAGE_BIT_HIDDEN 11 /* hidden by kmemcheck */ > #define _PAGE_BIT_PAT_LARGE 12 /* On 2MB or 1GB pages */ > #define _PAGE_BIT_SPECIAL _PAGE_BIT_UNUSED1 > @@ -41,7 +41,7 @@ > #define _PAGE_PSE (_AT(pteval_t, 1) << _PAGE_BIT_PSE) > #define _PAGE_GLOBAL (_AT(pteval_t, 1) << _PAGE_BIT_GLOBAL) > #define _PAGE_UNUSED1 (_AT(pteval_t, 1) << _PAGE_BIT_UNUSED1) > -#define _PAGE_IOMAP (_AT(pteval_t, 1) << _PAGE_BIT_IOMAP) > +#define _PAGE_UNUSED2 (_AT(pteval_t, 1) << _PAGE_BIT_UNUSED2) > #define _PAGE_PAT (_AT(pteval_t, 1) << _PAGE_BIT_PAT) > #define _PAGE_PAT_LARGE (_AT(pteval_t, 1) << _PAGE_BIT_PAT_LARGE) > #define _PAGE_SPECIAL (_AT(pteval_t, 1) << _PAGE_BIT_SPECIAL) > @@ -49,6 +49,13 @@ > #define _PAGE_SPLITTING (_AT(pteval_t, 1) << _PAGE_BIT_SPLITTING) > #define __HAVE_ARCH_PTE_SPECIAL > > +/* flag used to indicate IO mapping */ > +#ifdef CONFIG_XEN > +#define _PAGE_IOMAP (_AT(pteval_t, 1) << _PAGE_BIT_UNUSED2) > +#else > +#define _PAGE_IOMAP (_AT(pteval_t, 0)) > +#endif > + > #ifdef CONFIG_KMEMCHECK > #define _PAGE_HIDDEN (_AT(pteval_t, 1) << _PAGE_BIT_HIDDEN) > #else > -- > 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/