[PATCH 2/3] rfi-flush: Make it possible to call setup_rfi_flush() again

[Michal Suchánek]

On Tue, 06 Mar 2018 23:15:45 +1100
Michael Ellerman <mpe at ellerman.id.au> wrote:

> Mauricio Faria de Oliveira <mauricfo at linux.vnet.ibm.com> writes:
> 
> > Hi Michael, Michal,
> >
> > I got back from vacation. Checking this one.  
> 
> Yeah it got stuck in a rut.
> 
> > On 02/20/2018 02:06 PM, Michal Suchánek wrote:  
> >>> I did it the way I did because otherwise we waste memory on every
> >>> system on earth just to support a use case that we don't actually
> >>> intend for anyone to ever use - ie. migrating from a patched
> >>> machine to an unpatched machine.  
> >
> > If this thread eventually closes in 'ok, so that memory has to be
> > reserved/wasted anyway', that can be done only in pseries, right?
> >
> > It seems not so much memory for this particular platform/hardware.  
> 
> Yes and no. We certainly have pseries machines with 10s of TBs of
> memory, but pseries is also used when running on KVM/Openstack where
> some people are interested in running small VMs - so as usual it's not
> so simple :)
> 
> But it's not *that* much memory so we should probably stop worrying
> about it and just always allocate the fallback on pseries.
> 
> I *think* the patch below is all we need, as well as some tweaking of
> patch 2, are you able to test and repost?
> 
> cheers
> 
> diff --git a/arch/powerpc/platforms/pseries/setup.c
> b/arch/powerpc/platforms/pseries/setup.c index
> 1a527625acf7..9116824bd7c5 100644 ---
> a/arch/powerpc/platforms/pseries/setup.c +++
> b/arch/powerpc/platforms/pseries/setup.c @@ -468,26 +468,18 @@ static
> void pseries_setup_rfi_flush(void) 
>  	/* Enable by default */
>  	enable = true;
> +	types = L1D_FLUSH_FALLBACK;
>  
>  	rc = plpar_get_cpu_characteristics(&result);
>  	if (rc == H_SUCCESS) {
> -		types = L1D_FLUSH_NONE;
> -
>  		if (result.character & H_CPU_CHAR_L1D_FLUSH_TRIG2)
>  			types |= L1D_FLUSH_MTTRIG;
>  		if (result.character & H_CPU_CHAR_L1D_FLUSH_ORI30)
>  			types |= L1D_FLUSH_ORI;
>  
> -		/* Use fallback if nothing set in hcall */
> -		if (types == L1D_FLUSH_NONE)
> -			types = L1D_FLUSH_FALLBACK;
> -
>  		if ((!(result.behaviour & H_CPU_BEHAV_L1D_FLUSH_PR))
> || (!(result.behaviour & H_CPU_BEHAV_FAVOUR_SECURITY)))
>  			enable = false;
> -	} else {
> -		/* Default to fallback if case hcall is not
> available */
> -		types = L1D_FLUSH_FALLBACK;
>  	}
>  
>  	setup_rfi_flush(types, enable);
> 

Enabling the fallback flush always looks a bit dodgy but
do_rfi_flush_fixups will overwrite the jump so long any other fixup is
enabled.

Reviewed-by: Michal Suchánek <msuchanek at suse.de>

Thanks

Michal