Re: [Xen-devel] [PATCH] xen: arm: clear the exclusive monitor on exception return

[Tim Deegan <tim@xxxxxxx>]

At 12:18 +0100 on 17 Jul (1374063531), Ian Campbell wrote:
> Otherwise context switching between two vcpus which are contending the same
> lock can result in a spurious success.

Shouldn't this go in ctxt_swicth_to(), then?  I think any use that Xen
itself makes of the monitor should end with it cleared.

Tim.

> This is not required on ARMv8 since eret implicitly clears the monitor.
> 
> Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
> ---
>  xen/arch/arm/arm32/entry.S |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
> 
> diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S
> index 76814dd..1c26835 100644
> --- a/xen/arch/arm/arm32/entry.S
> +++ b/xen/arch/arm/arm32/entry.S
> @@ -117,6 +117,7 @@ ENTRY(return_to_hypervisor)
>          msr SPSR_hyp, r11
>          pop {r0-r12}
>          add sp, #(UREGS_SP_usr - UREGS_sp); /* SP, LR, SPSR, PC */
> +        clrex
>          eret
>  
>  /*
> -- 
> 1.7.2.5
> 
> 
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