Re: [PATCH v4 1/5] arm64: mte: Add asynchronous mode support

[Andrey Konovalov]

On Mon, Jan 18, 2021 at 7:30 PM Vincenzo Frascino
<vincenzo.frascino@xxxxxxx> wrote:
>
> MTE provides an asynchronous mode for detecting tag exceptions. In
> particular instead of triggering a fault the arm64 core updates a
> register which is checked by the kernel after the asynchronous tag
> check fault has occurred.
>
> Add support for MTE asynchronous mode.
>
> The exception handling mechanism will be added with a future patch.
>
> Note: KASAN HW activates async mode via kasan.mode kernel parameter.
> The default mode is set to synchronous.
> The code that verifies the status of TFSR_EL1 will be added with a
> future patch.
>
> Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
> Cc: Will Deacon <will@xxxxxxxxxx>
> Signed-off-by: Vincenzo Frascino <vincenzo.frascino@xxxxxxx>
> ---
>  arch/arm64/include/asm/memory.h    |  3 ++-
>  arch/arm64/include/asm/mte-kasan.h |  9 +++++++--
>  arch/arm64/kernel/mte.c            | 16 ++++++++++++++--
>  3 files changed, 23 insertions(+), 5 deletions(-)
>
> diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
> index 18fce223b67b..233d9feec45c 100644
> --- a/arch/arm64/include/asm/memory.h
> +++ b/arch/arm64/include/asm/memory.h
> @@ -231,7 +231,8 @@ static inline const void *__tag_set(const void *addr, u8 tag)
>  }
>
>  #ifdef CONFIG_KASAN_HW_TAGS
> -#define arch_enable_tagging()                  mte_enable_kernel()
> +#define arch_enable_tagging_sync()             mte_enable_kernel_sync()
> +#define arch_enable_tagging_async()            mte_enable_kernel_async()
>  #define arch_init_tags(max_tag)                        mte_init_tags(max_tag)
>  #define arch_get_random_tag()                  mte_get_random_tag()
>  #define arch_get_mem_tag(addr)                 mte_get_mem_tag(addr)
> diff --git a/arch/arm64/include/asm/mte-kasan.h b/arch/arm64/include/asm/mte-kasan.h
> index 26349a4b5e2e..9a5e30dbe12a 100644
> --- a/arch/arm64/include/asm/mte-kasan.h
> +++ b/arch/arm64/include/asm/mte-kasan.h
> @@ -29,7 +29,8 @@ u8 mte_get_mem_tag(void *addr);
>  u8 mte_get_random_tag(void);
>  void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag);
>
> -void mte_enable_kernel(void);
> +void mte_enable_kernel_sync(void);
> +void mte_enable_kernel_async(void);
>  void mte_init_tags(u64 max_tag);
>
>  #else /* CONFIG_ARM64_MTE */
> @@ -52,7 +53,11 @@ static inline void *mte_set_mem_tag_range(void *addr, size_t size, u8 tag)
>         return addr;
>  }
>
> -static inline void mte_enable_kernel(void)
> +static inline void mte_enable_kernel_sync(void)
> +{
> +}
> +
> +static inline void mte_enable_kernel_sync(void)
>  {
>  }
>
> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c
> index dc9ada64feed..78fc079a3b1e 100644
> --- a/arch/arm64/kernel/mte.c
> +++ b/arch/arm64/kernel/mte.c
> @@ -151,11 +151,23 @@ void mte_init_tags(u64 max_tag)
>         write_sysreg_s(SYS_GCR_EL1_RRND | gcr_kernel_excl, SYS_GCR_EL1);
>  }
>
> -void mte_enable_kernel(void)
> +static inline void __mte_enable_kernel(const char *mode, unsigned long tcf)
>  {
>         /* Enable MTE Sync Mode for EL1. */
> -       sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, SCTLR_ELx_TCF_SYNC);
> +       sysreg_clear_set(sctlr_el1, SCTLR_ELx_TCF_MASK, tcf);
>         isb();
> +
> +       pr_info_once("MTE: enabled in %s mode at EL1\n", mode);
> +}
> +
> +void mte_enable_kernel_sync(void)
> +{
> +       __mte_enable_kernel("synchronous", SCTLR_ELx_TCF_SYNC);
> +}
> +
> +void mte_enable_kernel_async(void)
> +{
> +       __mte_enable_kernel("asynchronous", SCTLR_ELx_TCF_ASYNC);
>  }
>
>  static void update_sctlr_el1_tcf0(u64 tcf0)
> --
> 2.30.0
>

Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxxx>