Subject: [PATCH 2/2] ARM: hyp: simplify __hyp_stub_install epilog

From: [email-masked] (Dave Martin)
Date: Mon, 7 Jan 2013 12:18:07 +0000

On Fri, Jan 04, 2013 at 05:44:15PM +0000, Marc Zyngier wrote:
> __hyp_stub_install duplicates quite a bit of safe_svcmode_maskall
> by forcing the CPU back to SVC. This is unnecessary, as
> safe_svcmode_maskall is called just after.
> 
> Furthermore, the way we build SPSR_hyp is buggy as we fail to mask
> the interrupts, leading to interesting behaviours on TC2 + UEFI.
> 
> The fix is to simply remove this code and rely on safe_svcmode_maskall
> to do the right thing.
> 
> Cc: Dave Martin <[email-masked]>
> Reported-by: Harry Liebel <[email-masked]>
> Signed-off-by: Marc Zyngier <[email-masked]>

Although there is clearly a bug here, it looks like interrupts will
promptly get masked afterwards due to save_svcmode_maskall.  This would
only fail if there is an interrupts asserted during this hazard ...?

Anyway, There's certainly no sense in trying to drop down to SVC mode
twice, so I agree that it is better to delegate that to the
save_svcmode_maskall macro.

Reviewed-by: Dave Martin <[email-masked]>

Cheers
---Dave

> ---
>  arch/arm/kernel/hyp-stub.S | 12 +++---------
>  1 file changed, 3 insertions(+), 9 deletions(-)
> 
> diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
> index 65b2417..da7e19f 100644
> --- a/arch/arm/kernel/hyp-stub.S
> +++ b/arch/arm/kernel/hyp-stub.S
> @@ -120,7 +120,8 @@ ENTRY(__hyp_stub_install_secondary)
>   * Eventually, CPU-specific code might be needed -- assume not for now
>   *
>   * This code relies on the "eret" instruction to synchronize the
> - * various coprocessor accesses.
> + * various coprocessor accesses. This is done when we switch to SVC
> + * (see safe_svcmode_maskall).
>   */
>  	@ Now install the hypervisor stub:
>  	adr	r7, __hyp_stub_vectors
> @@ -155,14 +156,7 @@ THUMB(	orr	r7, #(1 << 30)	)	@ HSCTLR.TE
>  1:
>  #endif
>  
> -	bic	r7, r4, #MODE_MASK
> -	orr	r7, r7, #SVC_MODE
> -THUMB(	orr	r7, r7, #PSR_T_BIT	)
> -	msr	spsr_cxsf, r7		@ This is SPSR_hyp.
> -
> -	__MSR_ELR_HYP(14)		@ msr elr_hyp, lr
> -	__ERET				@ return, switching to SVC mode
> -					@ The boot CPU mode is left in r4.
> +	bx	lr			@ The boot CPU mode is left in r4.
>  ENDPROC(__hyp_stub_install_secondary)
>  
>  __hyp_stub_do_trap:
> -- 
> 1.8.1
> 
>