2015-11-25 23:39 GMT+03:00 Daniel Cashman <dcashman@xxxxxxxxxxx>: > On 11/25/2015 04:06 AM, Catalin Marinas wrote: >> On Mon, Nov 23, 2015 at 10:55:16AM -0800, Daniel Cashman wrote: >>> On 11/23/2015 07:04 AM, Will Deacon wrote: >>>> On Wed, Nov 18, 2015 at 03:20:07PM -0800, Daniel Cashman wrote: >>>>> +config ARCH_MMAP_RND_BITS_MAX >>>>> + default 20 if ARM64_64K_PAGES && ARCH_VA_BITS=39 >> >> Where is ARCH_VA_BITS defined? We only have options like >> ARM64_VA_BITS_39. >> >> BTW, we no longer allow the 64K pages and 39-bit VA combination. > > It is not, and should have been ARM64_VA_BITS. This stanza was meant to > mimic the one for ARM64_VA_BITS. Thank you for pointing this, and the > 39-bit combination out. > >>>>> + default 24 if ARCH_VA_BITS=39 >>>>> + default 23 if ARM64_64K_PAGES && ARCH_VA_BITS=42 >>>>> + default 27 if ARCH_VA_BITS=42 >>>>> + default 29 if ARM64_64K_PAGES && ARCH_VA_BITS=48 >>>>> + default 33 if ARCH_VA_BITS=48 >>>>> + default 15 if ARM64_64K_PAGES >>>>> + default 19 >>>>> + >>>>> +config ARCH_MMAP_RND_COMPAT_BITS_MIN >>>>> + default 7 if ARM64_64K_PAGES >>>>> + default 11 >>>> >>>> FYI: we now support 16k pages too, so this might need updating. It would >>>> be much nicer if this was somehow computed rather than have the results >>>> all open-coded like this. >>> >>> Yes, I ideally wanted this to be calculated based on the different page >>> options and VA_BITS (which itself has a similar stanza), but I don't >>> know how to do that/if it is currently supported in Kconfig. This would >>> be even more desirable with the addition of 16K_PAGES, as with this >>> setup we have a combinatorial problem. >> >> For KASan, we ended up calculating KASAN_SHADOW_OFFSET in >> arch/arm64/Makefile. What would the formula be for the above >> ARCH_MMAP_RND_BITS_MAX? > > The general formula I used ended up being: > _max = floor(log(TASK_SIZE)) - log(PAGE_SIZE) - 3 > For kasan, we calculate KASAN_SHADOW_OFFSET in Makefile, because we need to use that value in Makefiles. For ARCH_MMAP_RND_COMPAT_BITS_MIN/MAX I don't see a reason why it has to be in Kconfig. Can't we just use your formula to #define ARCH_MMAP_RND_COMPAT_BITS_* in some arch header? > which in the case of arm64 ended up being VA_BITS - PAGE_SHIFT - 3. > Aside: following this would actually put COMPAT_BITS_MAX at 17 for 4k > pages, rather than 16, but I left it at 16 to mirror what was put in > arch/arm/Kconfig. > > > Thank You, > Dan > -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>