lkml.org 
[lkml]   [2016]   [Sep]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [RFC] arm64: Ensure proper addressing for ldnp/stnp
From
Date
On 09/19/2016 10:36 AM, Brent DeGraaf wrote:
> According to section 6.3.8 of the ARM Programmer's Guide, non-temporal
> loads and stores do not verify that address dependency is met between a
> load of an address to a register and a subsequent non-temporal load or
> store using that address on the executing PE. Therefore, context switch
> code and subroutine calls that use non-temporally accessed addresses as
> parameters that might depend on a load of an address into an argument
> register must ensure that ordering requirements are met by introducing
> a barrier prior to the successive non-temporal access. Add appropriate
> barriers whereever this specific situation comes into play.
>

Was this found by code inspection or is there a (public) exciting test
case to observe this behavior?

Thanks,
Laura

> Signed-off-by: Brent DeGraaf <bdegraaf@codeaurora.org>
> ---
> arch/arm64/kernel/entry.S | 1 +
> arch/arm64/lib/copy_page.S | 2 ++
> 2 files changed, 3 insertions(+)
>
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 441420c..982c4d3 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -679,6 +679,7 @@ ENTRY(cpu_switch_to)
> ldp x27, x28, [x8], #16
> ldp x29, x9, [x8], #16
> ldr lr, [x8]
> + dmb nshld // Existence of instructions with loose load-use dependencies (e.g. ldnp/stnp) make this barrier necessary
> mov sp, x9
> and x9, x9, #~(THREAD_SIZE - 1)
> msr sp_el0, x9
> diff --git a/arch/arm64/lib/copy_page.S b/arch/arm64/lib/copy_page.S
> index 4c1e700..21c6892 100644
> --- a/arch/arm64/lib/copy_page.S
> +++ b/arch/arm64/lib/copy_page.S
> @@ -47,6 +47,8 @@ alternative_endif
> ldp x14, x15, [x1, #96]
> ldp x16, x17, [x1, #112]
>
> + dmb nshld // In case x0 (for stnp) is dependent on a load
> +
> mov x18, #(PAGE_SIZE - 128)
> add x1, x1, #128
> 1:
>

\
 
 \ /
  Last update: 2016-09-19 20:29    [W:0.385 / U:0.064 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site