On 12/3/15 4:17 AM, Will Deacon wrote: >> + select HAVE_ARCH_MMAP_RND_BITS if MMU >> + select HAVE_ARCH_MMAP_RND_COMPAT_BITS if MMU && COMPAT > > You can drop the 'if MMU' bits, since we don't support !MMU on arm64. Ok, will do. I was a little uneasy leaving it implicit, but even if something w/out MMU on arm64 shows up, it'll easily be corrected. >> +config ARCH_MMAP_RND_BITS_MIN >> + default 15 if ARM64_64K_PAGES >> + default 17 if ARM64_16K_PAGES >> + default 19 > > Is this correct? We currently have a mask of 0x3ffff, so that's 18 bits. Off-by-one errors provide a good example of why hardening features are useful? =/ Will change. >> +config ARCH_MMAP_RND_BITS_MAX >> + default 19 if ARM64_VA_BITS=36 >> + default 20 if ARM64_64K_PAGES && ARM64_VA_BITS=39 >> + default 22 if ARM64_16K_PAGES && ARM64_VA_BITS=39 >> + default 24 if ARM64_VA_BITS=39 >> + default 23 if ARM64_64K_PAGES && ARM64_VA_BITS=42 >> + default 25 if ARM64_16K_PAGES && ARM64_VA_BITS=42 >> + default 27 if ARM64_VA_BITS=42 >> + default 30 if ARM64_VA_BITS=47 >> + default 29 if ARM64_64K_PAGES && ARM64_VA_BITS=48 >> + default 31 if ARM64_16K_PAGES && ARM64_VA_BITS=48 >> + default 33 if ARM64_VA_BITS=48 >> + default 15 if ARM64_64K_PAGES >> + default 17 if ARM64_16K_PAGES >> + default 19 > > Could you add a comment above this with the formula > (VA_BITS - PAGE_SHIFT - 3), please, so that we can update this easily in > the future if we need to? > Yes, seems reasonable. Time will tell if this remains true for all architectures, or even here, but it would be good to document it where someone considering a change could easily find it. 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>