[PATCH 4/4] kvm: powerpc: set cache coherency only for RAM pages

[Bhushan Bharat-R65777]

> -----Original Message-----
> From: Benjamin Herrenschmidt [mailto:benh at kernel.crashing.org]
> Sent: Friday, July 26, 2013 1:57 PM
> To: Bhushan Bharat-R65777
> Cc: kvm-ppc at vger.kernel.org; kvm at vger.kernel.org; linuxppc-dev at lists.ozlabs.org;
> agraf at suse.de; Wood Scott-B07421; Bhushan Bharat-R65777
> Subject: Re: [PATCH 4/4] kvm: powerpc: set cache coherency only for RAM pages
> 
> On Fri, 2013-07-26 at 11:16 +0530, Bharat Bhushan wrote:
> > If the page is RAM then map this as cacheable and coherent (set "M"
> > bit) otherwise this page is treated as I/O and map this as cache
> > inhibited and guarded (set  "I + G")
> >
> > This helps setting proper MMU mapping for direct assigned device.
> >
> > NOTE: There can be devices that require cacheable mapping, which is not yet
> supported.
> 
> Why don't you do like server instead and enforce the use of the same I and M
> bits as the corresponding qemu PTE ?

Ben/Alex, I will look into the code. Can you please describe how this is handled on server?

Thanks
-Bharat

> 
> Cheers,
> Ben.
> 
> > Signed-off-by: Bharat Bhushan <bharat.bhushan at freescale.com>
> > ---
> >  arch/powerpc/kvm/e500_mmu_host.c |   24 +++++++++++++++++++-----
> >  1 files changed, 19 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/powerpc/kvm/e500_mmu_host.c
> > b/arch/powerpc/kvm/e500_mmu_host.c
> > index 1c6a9d7..5cbdc8f 100644
> > --- a/arch/powerpc/kvm/e500_mmu_host.c
> > +++ b/arch/powerpc/kvm/e500_mmu_host.c
> > @@ -64,13 +64,27 @@ static inline u32 e500_shadow_mas3_attrib(u32 mas3, int
> usermode)
> >  	return mas3;
> >  }
> >
> > -static inline u32 e500_shadow_mas2_attrib(u32 mas2, int usermode)
> > +static inline u32 e500_shadow_mas2_attrib(u32 mas2, pfn_t pfn)
> >  {
> > +	u32 mas2_attr;
> > +
> > +	mas2_attr = mas2 & MAS2_ATTRIB_MASK;
> > +
> > +	if (kvm_is_mmio_pfn(pfn)) {
> > +		/*
> > +		 * If page is not RAM then it is treated as I/O page.
> > +		 * Map it with cache inhibited and guarded (set "I" + "G").
> > +		 */
> > +		mas2_attr |= MAS2_I | MAS2_G;
> > +		return mas2_attr;
> > +	}
> > +
> > +	/* Map RAM pages as cacheable (Not setting "I" in MAS2) */
> >  #ifdef CONFIG_SMP
> > -	return (mas2 & MAS2_ATTRIB_MASK) | MAS2_M;
> > -#else
> > -	return mas2 & MAS2_ATTRIB_MASK;
> > +	/* Also map as coherent (set "M") in SMP */
> > +	mas2_attr |= MAS2_M;
> >  #endif
> > +	return mas2_attr;
> >  }
> >
> >  /*
> > @@ -313,7 +327,7 @@ static void kvmppc_e500_setup_stlbe(
> >  	/* Force IPROT=0 for all guest mappings. */
> >  	stlbe->mas1 = MAS1_TSIZE(tsize) | get_tlb_sts(gtlbe) | MAS1_VALID;
> >  	stlbe->mas2 = (gvaddr & MAS2_EPN) |
> > -		      e500_shadow_mas2_attrib(gtlbe->mas2, pr);
> > +		      e500_shadow_mas2_attrib(gtlbe->mas2, pfn);
> >  	stlbe->mas7_3 = ((u64)pfn << PAGE_SHIFT) |
> >  			e500_shadow_mas3_attrib(gtlbe->mas7_3, pr);
> >
> 
>