Messages in this thread | | | Subject | Re: [Patch V6 12/16] mm: provide early_memremap_ro to establish read-only mapping | From | Juergen Gross <> | Date | Thu, 6 Aug 2015 15:02:09 +0200 |
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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 <jgross@suse.com> >> Acked-by: Konrad Rzeszutek Wilk <Konrad.wilk@oracle.com> >> Cc: Arnd Bergmann <arnd@arndb.de> >> 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
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