Re: [PATCH v7 1/2] arm64: Define Documentation/arm64/tagged-address-abi.rst

[Szabolcs Nagy <Szabolcs.Nagy@arm.com>]

On 07/08/2019 16:53, Catalin Marinas wrote:
> From: Vincenzo Frascino <vincenzo.frascino@arm.com>
> 
> On arm64 the TCR_EL1.TBI0 bit has been always enabled hence
> the userspace (EL0) is allowed to set a non-zero value in the
> top byte but the resulting pointers are not allowed at the
> user-kernel syscall ABI boundary.
> 
> With the relaxed ABI proposed through this document, it is now possible
> to pass tagged pointers to the syscalls, when these pointers are in
> memory ranges obtained by an anonymous (MAP_ANONYMOUS) mmap().

description needs to be updated not to restrict tags
to anon mmap.

> +3. AArch64 Tagged Address ABI Exceptions
> +-----------------------------------------
> +
> +The behaviour described in section 2, with particular reference to the
> +acceptance by the syscalls of any valid tagged pointer, is not applicable
> +to the following cases:
> +
> +- mmap() addr parameter.
> +
> +- mremap() new_address parameter.
> +
> +- prctl(PR_SET_MM, ``*``, ...) other than arg2 PR_SET_MM_MAP and
> +  PR_SET_MM_MAP_SIZE.
> +
> +- prctl(PR_SET_MM, PR_SET_MM_MAP{,_SIZE}, ...) struct prctl_mm_map fields.
> +
> +Any attempt to use non-zero tagged pointers will lead to undefined
> +behaviour.

i think that brk may be affected too by whatever that's
causing problems in mmap.

otherwise the text looks good to me.