Re: [PATCH v3 06/18] arm64: Do not enable uaccess for invalidate_icache_range

Mark Rutland
2021-05-20T14:16:09Z

On Thu, May 20, 2021 at 01:43:54PM +0100, Fuad Tabba wrote:
> invalidate_icache_range() works on the kernel linear map, and

Minor nit: this works on kernel addresses generally (e.g. vmalloc), so
we could say "kernel addresses" rather than "the kernel linear map".

> doesn't need uaccess. Remove the code that toggles
> uaccess_ttbr0_enable, as well as the code that emits an entry
> into the exception table (via the macro
> invalidate_icache_by_line).
>
> Changes return type of invalidate_icache_range() from int (which
> used to indicate a fault) to void, since it doesn't need uaccess
> and won't fault. Note that return value was never checked by any
> of the callers.
>
> No functional change intended.
> Possible performance impact due to the reduced number of
> instructions.
>
> Reported-by: Catalin Marinas <catalin.marinas@arm.com>
> Reported-by: Will Deacon <will@kernel.org>
> Link: https://lore.kernel.org/linux-arch/20200511110014.lb9PEahJ4hVOYrbwIb_qUHXyNy9KQzNFdb_I3YlzY6A@z/
> Signed-off-by: Fuad Tabba <tabba@google.com>

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
> arch/arm64/include/asm/cacheflush.h | 2 +-
> arch/arm64/mm/cache.S | 11 +----------
> 2 files changed, 2 insertions(+), 11 deletions(-)
>
> diff --git a/arch/arm64/include/asm/cacheflush.h b/arch/arm64/include/asm/cacheflush.h
> index 52e5c1623224..a586afa84172 100644
> --- a/arch/arm64/include/asm/cacheflush.h
> +++ b/arch/arm64/include/asm/cacheflush.h
> @@ -57,7 +57,7 @@
> * - size - region size
> */
> extern void __flush_icache_range(unsigned long start, unsigned long end);
> -extern int invalidate_icache_range(unsigned long start, unsigned long end);
> +extern void invalidate_icache_range(unsigned long start, unsigned long end);
> extern void __flush_dcache_area(void *addr, size_t len);
> extern void __inval_dcache_area(void *addr, size_t len);
> extern void __clean_dcache_area_poc(void *addr, size_t len);
> diff --git a/arch/arm64/mm/cache.S b/arch/arm64/mm/cache.S
> index c6bc3b8138e1..7318a40dd6ca 100644
> --- a/arch/arm64/mm/cache.S
> +++ b/arch/arm64/mm/cache.S
> @@ -97,21 +97,12 @@ SYM_FUNC_END(__flush_cache_user_range)
> */
> SYM_FUNC_START(invalidate_icache_range)
> alternative_if ARM64_HAS_CACHE_DIC
> - mov x0, xzr
> isb
> ret
> alternative_else_nop_endif
>
> - uaccess_ttbr0_enable x2, x3, x4
> -
> - invalidate_icache_by_line x0, x1, x2, x3, 2f
> - mov x0, xzr
> -1:
> - uaccess_ttbr0_disable x1, x2
> + invalidate_icache_by_line x0, x1, x2, x3
> ret
> -2:
> - mov x0, #-EFAULT
> - b 1b
> SYM_FUNC_END(invalidate_icache_range)
>
> /*
> --
> 2.31.1.751.gd2f1c929bd-goog