"Arnd Bergmann" <arnd@xxxxxxxx> writes: > On Mon, Sep 9, 2024, at 23:22, Charlie Jenkins wrote: >> On Fri, Sep 06, 2024 at 10:52:34AM +0100, Lorenzo Stoakes wrote: >>> On Fri, Sep 06, 2024 at 09:14:08AM GMT, Arnd Bergmann wrote: >>> The intent is to optionally be able to run a process that keeps higher bits >>> free for tagging and to be sure no memory mapping in the process will >>> clobber these (correct me if I'm wrong Charlie! :) ... > Let's see what the other architectures do and then come up with > a way that fixes the pointer tagging case first on those that are > broken. We can see if there needs to be an extra flag after that. > Here is what I found: > > - x86_64 uses DEFAULT_MAP_WINDOW of BIT(47), uses a 57 bit > address space when an addr hint is passed. > - arm64 uses DEFAULT_MAP_WINDOW of BIT(47) or BIT(48), returns > higher 52-bit addresses when either a hint is passed or > CONFIG_EXPERT and CONFIG_ARM64_FORCE_52BIT is set (this > is a debugging option) > - ppc64 uses a DEFAULT_MAP_WINDOW of BIT(47) or BIT(48), > returns 52 bit address when an addr hint is passed It's 46 or 47 depending on PAGE_SIZE (4K or 64K): $ git grep "define DEFAULT_MAP_WINDOW_USER64" arch/powerpc/include/asm/task_size_64.h arch/powerpc/include/asm/task_size_64.h:#define DEFAULT_MAP_WINDOW_USER64 TASK_SIZE_128TB arch/powerpc/include/asm/task_size_64.h:#define DEFAULT_MAP_WINDOW_USER64 TASK_SIZE_64TB cheers
