Re: [PATCH 0/5] arm64: ARMv8.7-A: MTE: Add asymm mode support

[Will Deacon]

On Mon, Sep 13, 2021 at 09:14:19AM +0100, Vincenzo Frascino wrote:
> This series implements the asymmetric mode support for ARMv8.7-A Memory
> Tagging Extension (MTE), which is a debugging feature that allows to
> detect with the help of the architecture the C and C++ programmatic
> memory errors like buffer overflow, use-after-free, use-after-return, etc.
> 
> MTE is built on top of the AArch64 v8.0 virtual address tagging TBI
> (Top Byte Ignore) feature and allows a task to set a 4 bit tag on any
> subset of its address space that is multiple of a 16 bytes granule. MTE
> is based on a lock-key mechanism where the lock is the tag associated to
> the physical memory and the key is the tag associated to the virtual
> address.
> 
> When MTE is enabled and tags are set for ranges of address space of a task,
> the PE will compare the tag related to the physical memory with the tag
> related to the virtual address (tag check operation). Access to the memory
> is granted only if the two tags match. In case of mismatch the PE will raise
> an exception.
> 
> When asymmetric mode is present, the CPU triggers a fault on a tag mismatch
> during a load operation and asynchronously updates a register when a tag
> mismatch is detected during a store operation.
> 
> The series is based on linux-v5.15-rc1.
> 
> To simplify the testing a tree with the new patches on top has been made
> available at [1].
> 
> [1] https://git.gitlab.arm.com/linux-arm/linux-vf.git mte/v1.asymm
> 
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx>
> Cc: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Evgenii Stepanov <eugenis@xxxxxxxxxx>
> Cc: Branislav Rankov <Branislav.Rankov@xxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> 
> Vincenzo Frascino (5):
>   kasan: Remove duplicate of kasan_flag_async
>   arm64: mte: Bitfield definitions for Asymm MTE
>   arm64: mte: CPU feature detection for Asymm MTE
>   arm64: mte: Add asymmetric mode support
>   kasan: Extend KASAN mode kernel parameter
> 
>  Documentation/dev-tools/kasan.rst  | 10 ++++++++--

I'm surprised not to see any update to:

	Documentation/arm64/memory-tagging-extension.rst

particularly regarding the per-cpu preferred tag checking modes. Is
asymmetric mode not supported there?

Will