Messages in this thread Patch in this message | | | Date | Tue, 18 Nov 2014 21:13:56 +0300 | From | Konstantin Khlebnikov <> | Subject | Re: [PATCH RFC] ARM: option for loading modules into vmalloc area |
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On 2014-11-18 20:34, Russell King - ARM Linux wrote: > On Tue, Nov 18, 2014 at 08:21:46PM +0400, Konstantin Khlebnikov wrote: >> Usually modules are loaded into small area prior to the kernel >> text because they are linked with the kernel using short calls. >> Compile-time instrumentation like GCOV or KASAN bloats code a lot, >> and as a result huge modules no longer fit into reserved area. >> >> This patch adds option CONFIG_MODULES_USE_VMALLOC which lifts >> limitation on amount of loaded modules. It links modules using >> long-calls (option -mlong-calls) and loads them into vmalloc area. >> >> In few places exported symbols are called from inline assembly. >> This patch adds macro for such call sites: __asmbl and __asmbl_clobber. >> Call turns into single 'bl' or sequence 'movw; movt; blx' depending on >> context and state of config option. >> >> Unfortunately this option isn't compatible with CONFIG_FUNCTION_TRACER. >> Compiler emits short calls to profiling function despite of -mlong-calls. >> This is a bug in GCC, but ftrace anyway needs an update to handle this. > It also isn't compatible with the older architectures which don't have > "blx".
Ok, I'll add "depends on CPU_V6 || CPU_V7" I don't think that it is necessary for older cpus.
>> diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c >> index 9d2cdda..9e0c4f4 100644 >> --- a/arch/arm/mm/mmu.c >> +++ b/arch/arm/mm/mmu.c >> @@ -1161,16 +1161,15 @@ void __init sanity_check_meminfo(void) >> >> static inline void prepare_page_table(void) >> { >> - unsigned long addr; >> + unsigned long addr = 0; >> phys_addr_t end; >> >> /* >> * Clear out all the mappings below the kernel image. >> */ >> - for (addr = 0; addr < MODULES_VADDR; addr += PMD_SIZE) >> - pmd_clear(pmd_off_k(addr)); >> - >> #ifdef CONFIG_XIP_KERNEL >> + for ( ; addr < MODULES_VADDR; addr += PMD_SIZE) >> + pmd_clear(pmd_off_k(addr)); >> /* The XIP kernel is mapped in the module area -- skip over it */ >> addr = ((unsigned long)_etext + PMD_SIZE - 1) & PMD_MASK; >> #endif > This seems to be an unrelated change. In any case, it looks wrong to > me. Please describe what you are trying to achieve here. >
My patch changes MODULES_VADDR, if option enabled it becomes alias for VMALLOC_START
It's used as border between two loops, before patch this code looks like:
/* * Clear out all the mappings below the kernel image. */ for (addr = 0; addr < MODULES_VADDR; addr += PMD_SIZE) pmd_clear(pmd_off_k(addr));
#ifdef CONFIG_XIP_KERNEL /* The XIP kernel is mapped in the module area -- skip over it */ addr = ((unsigned long)_etext + PMD_SIZE - 1) & PMD_MASK; #endif for ( ; addr < PAGE_OFFSET; addr += PMD_SIZE) pmd_clear(pmd_off_k(addr));
It's written with assumption that MODULES_VADDR < PAGE_OFFSET, but this no longer true if modules are placed inside vmalloc area.
After patch: unsigned long addr = 0;
/* * Clear out all the mappings below the kernel image. */ #ifdef CONFIG_XIP_KERNEL for ( ; addr < MODULES_VADDR; addr += PMD_SIZE) pmd_clear(pmd_off_k(addr)); /* The XIP kernel is mapped in the module area -- skip over it */ addr = ((unsigned long)_etext + PMD_SIZE - 1) & PMD_MASK; #endif for ( ; addr < PAGE_OFFSET; addr += PMD_SIZE) pmd_clear(pmd_off_k(addr));
Without XIP there is no reason for splitting it into two loops.
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