Messages in this thread | | | Date | Fri, 08 Feb 2013 15:16:18 -0800 | From | Dave Hansen <> | Subject | Re: [PATCH 1/2] add helper for highmem checks |
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On 02/08/2013 12:50 PM, H. Peter Anvin wrote: > On 02/08/2013 12:28 PM, Dave Hansen wrote: >> +static inline phys_addr_t last_lowmem_phys_addr(void) >> +{ >> + /* >> + * 'high_memory' is not a pointer that can be dereferenced, so >> + * avoid calling __pa() on it directly. >> + */ >> + return __pa(high_memory - 1); >> +} >> +static inline bool phys_addr_is_highmem(phys_addr_t addr) >> +{ >> + return addr > last_lowmem_paddr(); >> +} >> + > > Are we sure that high_memory - 1 is always a valid reference? Consider > especially the case where there is MMIO beyond end of memory on a system > which has less RAM than the HIGHMEM boundary...
Yeah, I think it is. "high_memory" should point at either the end of RAM, or the end of the linear map, whichever is lower. See setup_arch():
max_pfn = e820_end_of_ram_pfn(); ... high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
or in the highmem init code:
high_memory = (void *) __va(max_low_pfn * PAGE_SIZE - 1) + 1;
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