On 13/08/18 05:30 PM, Kit Chow wrote: > In arch/x86/include/asm/page.h, there is the following comment in > regards to validating the virtual address. > > /* > * virt_to_page(kaddr) returns a valid pointer if and only if > * virt_addr_valid(kaddr) returns true. > */ > #define virt_to_page(kaddr) pfn_to_page(__pa(kaddr) >> PAGE_SHIFT) > > So it looks like the validation by virt_addr_valid was somehow dropped > from the virt_to_page code path. Does anyone have any ideas what > happended to it? I don't think it was ever validated (though I haven't been around long enough to say for certain). What the comment is saying is that you shouldn't rely on virt_to_page() unless you know virt_addr_valid() is true (which in most cases you can without the extra check). virt_to_page is meant to be really fast so adding an extra validation would probably be a significant performance regression for the entire kernel. The fact that this can happen through dma_map_single() is non-ideal at best. It assumes the caller is mapping regular memory and doesn't check this at all. It may make sense to fix that but I think people expect dma_map_single() to be as fast as possible as well... Logan
