Re: [PATCH v7 2/2] arm64: Relax Documentation/arm64/tagged-pointers.rst

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On Wed, Aug 07, 2019 at 04:53:21PM +0100, Catalin Marinas wrote:
> From: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> 
> 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 in this set, 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().
> 
> Relax the requirements described in tagged-pointers.rst to be compliant
> with the behaviours guaranteed by the ARM64 Tagged Address ABI.
> 
> Cc: Will Deacon <will.deacon@xxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Cc: Szabolcs Nagy <szabolcs.nagy@xxxxxxx>
> Cc: Kevin Brodsky <kevin.brodsky@xxxxxxx>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> [catalin.marinas@xxxxxxx: minor tweaks]
> Signed-off-by: Catalin Marinas <catalin.marinas@xxxxxxx>
> ---
>  Documentation/arm64/tagged-pointers.rst | 23 ++++++++++++++++-------
>  1 file changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/arm64/tagged-pointers.rst b/Documentation/arm64/tagged-pointers.rst
> index 2acdec3ebbeb..82a3eff71a70 100644
> --- a/Documentation/arm64/tagged-pointers.rst
> +++ b/Documentation/arm64/tagged-pointers.rst
> @@ -20,7 +20,8 @@ Passing tagged addresses to the kernel
>  --------------------------------------
>  
>  All interpretation of userspace memory addresses by the kernel assumes
> -an address tag of 0x00.
> +an address tag of 0x00, unless the application enables the AArch64
> +Tagged Address ABI explicitly.

I think we should have the link to Documentation/arm64/tagged-address-abi.rst
here so people see it when it's first referenced.

> +The AArch64 Tagged Address ABI description and the guarantees it
> +provides can be found in: Documentation/arm64/tagged-address-abi.rst.

Then this sentence can be dropped.

Will



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