Re: [PATCH 09/14] powerpc/rtas: Leave MSR[RI] enabled over RTAS call

[Laurent Dufour <ldufour@linux.ibm.com>]

On 08/03/2022, 14:50:42, Nicholas Piggin wrote:
> PAPR specifies that RTAS may be called with MSR[RI] enabled if the
> calling context is recoverable, and RTAS will manage RI as necessary.
> Call the rtas entry point with RI enabled, and add a check to ensure
> the caller has RI enabled.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> ---
>  arch/powerpc/kernel/rtas.c       |  1 +
>  arch/powerpc/kernel/rtas_entry.S | 13 +++----------
>  2 files changed, 4 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
> index 87ede1877816..fece066115f0 100644
> --- a/arch/powerpc/kernel/rtas.c
> +++ b/arch/powerpc/kernel/rtas.c
> @@ -57,6 +57,7 @@ static noinline void do_enter_rtas(unsigned long args)
>  		hard_irq_disable();
>  
>  		msr = mfmsr();
> +		BUG_ON(!(msr & MSR_RI));
>  		mtmsr(msr & ~(MSR_IR|MSR_DR));
>  		enter_rtas(args);
>  		mtmsr(msr);
> diff --git a/arch/powerpc/kernel/rtas_entry.S b/arch/powerpc/kernel/rtas_entry.S
> index 292551684bbd..72b27b14ccc9 100644
> --- a/arch/powerpc/kernel/rtas_entry.S
> +++ b/arch/powerpc/kernel/rtas_entry.S
> @@ -95,7 +95,7 @@ _GLOBAL(enter_rtas)
>  	clrldi	r4,r4,2			/* convert to realmode address */
>  	mtlr	r4
>  
> -	LOAD_REG_IMMEDIATE(r6, MSR_ME)
> +	LOAD_REG_IMMEDIATE(r6, MSR_ME|MSR_RI)
>  
>  	LOAD_REG_ADDR(r4, rtas)
>  	ld	r5,RTASENTRY(r4)	/* get the rtas->entry value */
> @@ -113,15 +113,8 @@ _ASM_NOKPROBE_SYMBOL(enter_rtas)
>  rtas_return_loc:
>  	FIXUP_ENDIAN
>  
> -	/*
> -	 * Clear RI and set SF before anything.
> -	 */
> -	mfmsr	r6
> -	li	r0,MSR_RI
> -	andc	r6,r6,r0
> -	sldi	r0,r0,(MSR_SF_LG - MSR_RI_LG)
> -	or	r6,r6,r0
> -	sync
> +	/* Set SF before anything. */
> +	LOAD_REG_IMMEDIATE(r6, MSR_KERNEL & ~(MSR_IR|MSR_DR))

I guess we cannot directly load a MSR value stored in the PACA at that
time, isn't it?

>  	mtmsrd	r6
>  
>  	GET_PACA(r13)