Subject: Re: [PATCH 05/12] powerpc/64s/hash: Use POWER6 SLBIA IH=1 variant in switch_slb

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Mon, 17 Sep 2018 11:38:35 +0530

Nicholas Piggin <[email-masked]> writes:

> The SLBIA IH=1 hint will remove all non-zero SLBEs, but only
> invalidate ERAT entries associated with a class value of 1, for
> processors that support the hint (e.g., POWER6 and newer), which
> Linux assigns to user addresses.
>
> This prevents kernel ERAT entries from being invalidated when
> context switchig (if the thread faulted in more than 8 user SLBEs).

how about renaming stuff to indicate kernel ERAT entries are kept?
something like slb_flush_and_rebolt_user()? 

>
> Signed-off-by: Nicholas Piggin <[email-masked]>
> ---
>  arch/powerpc/mm/slb.c | 38 +++++++++++++++++++++++---------------
>  1 file changed, 23 insertions(+), 15 deletions(-)
>
> diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c
> index a5e58f11d676..03fa1c663ccf 100644
> --- a/arch/powerpc/mm/slb.c
> +++ b/arch/powerpc/mm/slb.c
> @@ -128,13 +128,21 @@ void slb_flush_all_realmode(void)
>  	asm volatile("slbmte %0,%0; slbia" : : "r" (0));
>  }
>  
> -static void __slb_flush_and_rebolt(void)
> +void slb_flush_and_rebolt(void)
>  {
>  	/* If you change this make sure you change SLB_NUM_BOLTED
>  	 * and PR KVM appropriately too. */
>  	unsigned long linear_llp, lflags;
>  	unsigned long ksp_esid_data, ksp_vsid_data;
>  
> +	WARN_ON(!irqs_disabled());
> +
> +	/*
> +	 * We can't take a PMU exception in the following code, so hard
> +	 * disable interrupts.
> +	 */
> +	hard_irq_disable();
> +
>  	linear_llp = mmu_psize_defs[mmu_linear_psize].sllp;
>  	lflags = SLB_VSID_KERNEL | linear_llp;
>  
> @@ -160,20 +168,7 @@ static void __slb_flush_and_rebolt(void)
>  		     :: "r"(ksp_vsid_data),
>  		        "r"(ksp_esid_data)
>  		     : "memory");
> -}
>  
> -void slb_flush_and_rebolt(void)
> -{
> -
> -	WARN_ON(!irqs_disabled());
> -
> -	/*
> -	 * We can't take a PMU exception in the following code, so hard
> -	 * disable interrupts.
> -	 */
> -	hard_irq_disable();
> -
> -	__slb_flush_and_rebolt();
>  	get_paca()->slb_cache_ptr = 0;
>  }
>  
> @@ -248,7 +243,20 @@ void switch_slb(struct task_struct *tsk, struct mm_struct *mm)
>  
>  		asm volatile("isync" : : : "memory");
>  	} else {
> -		__slb_flush_and_rebolt();
> +		struct slb_shadow *p = get_slb_shadow();
> +		unsigned long ksp_esid_data =
> +			be64_to_cpu(p->save_area[KSTACK_INDEX].esid);
> +		unsigned long ksp_vsid_data =
> +			be64_to_cpu(p->save_area[KSTACK_INDEX].vsid);
> +
> +		asm volatile("isync\n"
> +			     PPC_SLBIA(1) "\n"
> +			     "slbmte	%0,%1\n"
> +			     "isync"
> +			     :: "r"(ksp_vsid_data),
> +				"r"(ksp_esid_data));
> +
> +		asm volatile("isync" : : : "memory");
>  	}
>  
>  	get_paca()->slb_cache_ptr = 0;
> -- 
> 2.18.0