linux-kernel - Re: [PATCH 10/15] powerpc/mm: Add hooks for cxl

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Message-ID: <20140926143309.33c0eeac@kryten>
Date:	Fri, 26 Sep 2014 14:33:09 +1000
From:	Anton Blanchard <anton@...ba.org>
To:	Michael Neuling <mikey@...ling.org>
Cc:	greg@...ah.com, arnd@...db.de, mpe@...erman.id.au,
	benh@...nel.crashing.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...abs.org, jk@...abs.org, imunsie@...ibm.com,
	cbe-oss-dev@...ts.ozlabs.org
Subject: Re: [PATCH 10/15] powerpc/mm: Add hooks for cxl

> From: Ian Munsie <imunsie@....ibm.com>
> 
> This add a hook into tlbie() so that we use global invalidations when
> there are cxl contexts active.
> 
> Normally cxl snoops broadcast tlbie.  cxl can have TLB entries
> invalidated via MMIO, but we aren't doing that yet.  So for now we
> are just disabling local tlbies when cxl contexts are active.  In
> future we can make tlbie() local mode smarter so that it invalidates
> cxl contexts explicitly when it needs to.
> 
> This also adds a hooks for when SLBs are invalidated to ensure any
> corresponding SLBs in cxl are also invalidated at the same time.
> 
> Signed-off-by: Ian Munsie <imunsie@....ibm.com>
> Signed-off-by: Michael Neuling <mikey@...ling.org>

> +	use_local = local && mmu_has_feature(MMU_FTR_TLBIEL) && !cxl_ctx_in_use();

Seems reasonable until we can get the MMIO based optimisation in.

Will all CAPI cached translations be invalidated before we finish using
a CAPI context? And conversely, could CAPI cache any translations when a
context isn't active? I'm mostly concerned that we can't have a
situation where badly behaving userspace could result in a stale
translation.

>  	spu_flush_all_slbs(mm);
>  #endif
> +	cxl_slbia(mm);

>  			spu_flush_all_slbs(mm);
>  #endif
> +			cxl_slbia(mm);

>  	spu_flush_all_slbs(mm);
>  #endif
> +	cxl_slbia(mm);

>  	spu_flush_all_slbs(mm);
>  #endif
> +	cxl_slbia(mm);

Should we combine the SPU vs CXL callouts into something common -
perhaps copro_flush_all_slbs()?

Anton
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