Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755548AbbHFNCN (ORCPT ); Thu, 6 Aug 2015 09:02:13 -0400 Received: from mx2.suse.de ([195.135.220.15]:42098 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750758AbbHFNCM (ORCPT ); Thu, 6 Aug 2015 09:02:12 -0400 Subject: Re: [Patch V6 12/16] mm: provide early_memremap_ro to establish read-only mapping To: Vlastimil Babka , linux-kernel@vger.kernel.org, xen-devel@lists.xensource.com, konrad.wilk@oracle.com, david.vrabel@citrix.com, boris.ostrovsky@oracle.com References: <1437108697-4115-1-git-send-email-jgross@suse.com> <1437108697-4115-13-git-send-email-jgross@suse.com> <55C3573B.6020509@suse.cz> Cc: Arnd Bergmann , linux-mm@kvack.org, linux-arch@vger.kernel.org From: Juergen Gross Message-ID: <55C35AD1.7010101@suse.com> Date: Thu, 6 Aug 2015 15:02:09 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.1.0 MIME-Version: 1.0 In-Reply-To: <55C3573B.6020509@suse.cz> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4421 Lines: 121 On 08/06/2015 02:46 PM, Vlastimil Babka wrote: > On 07/17/2015 06:51 AM, Juergen Gross wrote: >> During early boot as Xen pv domain the kernel needs to map some page >> tables supplied by the hypervisor read only. This is needed to be >> able to relocate some data structures conflicting with the physical >> memory map especially on systems with huge RAM (above 512GB). >> >> Provide the function early_memremap_ro() to provide this read only >> mapping. >> >> Signed-off-by: Juergen Gross >> Acked-by: Konrad Rzeszutek Wilk >> Cc: Arnd Bergmann >> Cc: linux-mm@kvack.org >> Cc: linux-arch@vger.kernel.org >> --- >> include/asm-generic/early_ioremap.h | 2 ++ >> include/asm-generic/fixmap.h | 3 +++ >> mm/early_ioremap.c | 12 ++++++++++++ >> 3 files changed, 17 insertions(+) >> >> diff --git a/include/asm-generic/early_ioremap.h >> b/include/asm-generic/early_ioremap.h >> index a5de55c..316bd04 100644 >> --- a/include/asm-generic/early_ioremap.h >> +++ b/include/asm-generic/early_ioremap.h >> @@ -11,6 +11,8 @@ extern void __iomem *early_ioremap(resource_size_t >> phys_addr, >> unsigned long size); >> extern void *early_memremap(resource_size_t phys_addr, >> unsigned long size); >> +extern void *early_memremap_ro(resource_size_t phys_addr, >> + unsigned long size); > > So the function is declared unconditionally... > >> extern void early_iounmap(void __iomem *addr, unsigned long size); >> extern void early_memunmap(void *addr, unsigned long size); >> >> diff --git a/include/asm-generic/fixmap.h b/include/asm-generic/fixmap.h >> index f23174f..1cbb833 100644 >> --- a/include/asm-generic/fixmap.h >> +++ b/include/asm-generic/fixmap.h >> @@ -46,6 +46,9 @@ static inline unsigned long virt_to_fix(const >> unsigned long vaddr) >> #ifndef FIXMAP_PAGE_NORMAL >> #define FIXMAP_PAGE_NORMAL PAGE_KERNEL >> #endif >> +#if !defined(FIXMAP_PAGE_RO) && defined(PAGE_KERNEL_RO) >> +#define FIXMAP_PAGE_RO PAGE_KERNEL_RO >> +#endif >> #ifndef FIXMAP_PAGE_NOCACHE >> #define FIXMAP_PAGE_NOCACHE PAGE_KERNEL_NOCACHE >> #endif >> diff --git a/mm/early_ioremap.c b/mm/early_ioremap.c >> index e10ccd2..0cfadaf 100644 >> --- a/mm/early_ioremap.c >> +++ b/mm/early_ioremap.c >> @@ -217,6 +217,13 @@ early_memremap(resource_size_t phys_addr, >> unsigned long size) >> return (__force void *)__early_ioremap(phys_addr, size, >> FIXMAP_PAGE_NORMAL); >> } >> +#ifdef FIXMAP_PAGE_RO >> +void __init * >> +early_memremap_ro(resource_size_t phys_addr, unsigned long size) >> +{ >> + return (__force void *)__early_ioremap(phys_addr, size, >> FIXMAP_PAGE_RO); >> +} >> +#endif > > ... here we provide a implementation when both CONFIG_MMU and > FIXMAP_PAGE_RO are defined... > >> #else /* CONFIG_MMU */ >> >> void __init __iomem * >> @@ -231,6 +238,11 @@ early_memremap(resource_size_t phys_addr, >> unsigned long size) >> { >> return (void *)phys_addr; >> } >> +void __init * >> +early_memremap_ro(resource_size_t phys_addr, unsigned long size) >> +{ >> + return (void *)phys_addr; >> +} > > ... and here for !CONFIG_MMU. > > So, what about CONFIG_MMU && !FIXMAP_PAGE_RO combinations? Which > translates to CONFIG_MMU && !PAGE_KERNEL_RO. Maybe they don't exist, but > then it's still awkward to see the combination in the code left > unimplemented. At least there are some architectures without #define PAGE_KERNEL_RO but testing CONFIG_MMU (arm, m68k, xtensa). > Would it be perhaps simpler to assume the same thing as in > drivers/base/firmware_class.c ? > > /* Some architectures don't have PAGE_KERNEL_RO */ > #ifndef PAGE_KERNEL_RO > #define PAGE_KERNEL_RO PAGE_KERNEL > #endif > > Or would it be dangerous here to silently lose the read-only protection? The only reason to use this function instead of early_memremap() is the mandatory read-only mapping. My intention was to let the build fail in case it is being used but not implemented. An architecture requiring the function but having no PAGE_KERNEL_RO still can define FIXMAP_PAGE_RO. Juergen -- 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/