Subject: Re: [PATCH] powerpc: add the missing required isync for the coherent icache flush

From: Benjamin Herrenschmidt <[email-masked]>
Date: Mon, 19 Aug 2013 13:36:37 +1000

On Mon, 2013-08-19 at 03:24 +0000, Wang Dongsheng-B40534 wrote:
> 
> > -----Original Message-----
> > From: Linuxppc-dev [mailto:linuxppc-dev-
> > bounces+b40534=[email-masked]] On Behalf Of Kevin Hao
> > Sent: Thursday, August 15, 2013 7:56 PM
> > To: Benjamin Herrenschmidt
> > Cc: linuxppc
> > Subject: [PATCH] powerpc: add the missing required isync for the coherent
> > icache flush
> > 
> > Even we don't need to flush the dcache and invalidate the icache
> > on the CPU which has coherent icache. But we do need an isync to
> > discard the prefetched instructions in this case.
> > 
> > Signed-off-by: Kevin Hao <[email-masked]>
> > ---
> >  arch/powerpc/kernel/misc_32.S | 2 ++
> >  arch/powerpc/kernel/misc_64.S | 1 +
> >  2 files changed, 3 insertions(+)
> > 
> > diff --git a/arch/powerpc/kernel/misc_32.S
> > b/arch/powerpc/kernel/misc_32.S
> > index 777d999..0b84c8d 100644
> > --- a/arch/powerpc/kernel/misc_32.S
> > +++ b/arch/powerpc/kernel/misc_32.S
> > @@ -433,6 +433,7 @@ _GLOBAL(invalidate_dcache_range)
> >   */
> >  _GLOBAL(__flush_dcache_icache)
> >  BEGIN_FTR_SECTION
> > +	isync
> There is not touch the icache, why need we to do this?

The semantic of this function is to make data executable. Even if the
implementation has a snooping icache, it *still* needs to make sure
prefetched code is tossed out of the pipeline which is what isync
should provide.

The architecture actually specifies that.

Cheers,
Ben.

> >  	blr
> >  END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_ICACHE)
> >  	rlwinm	r3,r3,0,0,31-PAGE_SHIFT		/* Get page base address
> > */
> > @@ -474,6 +475,7 @@ END_MMU_FTR_SECTION_IFSET(MMU_FTR_TYPE_44x)
> >   */
> >  _GLOBAL(__flush_dcache_icache_phys)
> >  BEGIN_FTR_SECTION
> > +	isync
> >  	blr					/* for 601, do nothing */
> >  END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_ICACHE)
> >  	mfmsr	r10
> > diff --git a/arch/powerpc/kernel/misc_64.S
> > b/arch/powerpc/kernel/misc_64.S
> > index 992a78e..d74fefb 100644
> > --- a/arch/powerpc/kernel/misc_64.S
> > +++ b/arch/powerpc/kernel/misc_64.S
> > @@ -69,6 +69,7 @@ PPC64_CACHES:
> > 
> >  _KPROBE(flush_icache_range)
> >  BEGIN_FTR_SECTION
> > +	isync
> >  	blr
> >  END_FTR_SECTION_IFSET(CPU_FTR_COHERENT_ICACHE)
> >  /*
> > --
> > 1.8.3.1
> > 
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