[PATCH v5 4/6] arm64: mte: Enable async tag check fault

[Catalin Marinas]

On Thu, Jan 21, 2021 at 04:39:41PM +0000, Vincenzo Frascino wrote:
> MTE provides a mode that asynchronously updates the TFSR_EL1 register
> when a tag check exception is detected.
> 
> To take advantage of this mode the kernel has to verify the status of
> the register at:
>   1. Context switching
>   2. Return to user/EL0 (Not required in entry from EL0 since the kernel
>   did not run)
>   3. Kernel entry from EL1
>   4. Kernel exit to EL1
> 
> If the register is non-zero a trace is reported.
> 
> Add the required features for EL1 detection and reporting.
> 
> Note: ITFSB bit is set in the SCTLR_EL1 register hence it guaranties that
> the indirect writes to TFSR_EL1 are synchronized at exception entry to
> EL1. On the context switch path the synchronization is guarantied by the
> dsb() in __switch_to().
> The dsb(nsh) in mte_check_tfsr_exit() is provisional pending
> confirmation by the architects.
> 
> Cc: Catalin Marinas <catalin.marinas at arm.com>
> Cc: Will Deacon <will at kernel.org>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino at arm.com>

Reviewed-by: Catalin Marinas <catalin.marinas at arm.com>