RE: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel managed pages

[Bhushan Bharat-R65777 <R65777@freescale.com>]

> -----Original Message-----
> From: kvm-ppc-owner@vger.kernel.org [mailto:kvm-ppc-owner@vger.kernel.org] On
> Behalf Of "“tiejun.chen”"
> Sent: Thursday, July 18, 2013 1:01 PM
> To: Bhushan Bharat-R65777
> Cc: kvm-ppc@vger.kernel.org; kvm@vger.kernel.org; agraf@suse.de; Wood Scott-
> B07421
> Subject: Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for kernel
> managed pages
> 
> On 07/18/2013 03:12 PM, Bhushan Bharat-R65777 wrote:
> >
> >
> >> -----Original Message-----
> >> From: "“tiejun.chen”" [mailto:tiejun.chen@windriver.com]
> >> Sent: Thursday, July 18, 2013 11:56 AM
> >> To: Bhushan Bharat-R65777
> >> Cc: kvm-ppc@vger.kernel.org; kvm@vger.kernel.org; agraf@suse.de; Wood
> >> Scott- B07421; Bhushan Bharat-R65777
> >> Subject: Re: [PATCH 2/2] kvm: powerpc: set cache coherency only for
> >> kernel managed pages
> >>
> >> On 07/18/2013 02:04 PM, Bharat Bhushan wrote:
> >>> If there is a struct page for the requested mapping then it's normal
> >>> DDR and the mapping sets "M" bit (coherent, cacheable) else this is
> >>> treated as I/O and we set  "I + G"  (cache inhibited, guarded)
> >>>
> >>> This helps setting proper TLB mapping for direct assigned device
> >>>
> >>> Signed-off-by: Bharat Bhushan <bharat.bhushan@freescale.com>
> >>> ---
> >>>    arch/powerpc/kvm/e500_mmu_host.c |   17 ++++++++++++-----
> >>>    1 files changed, 12 insertions(+), 5 deletions(-)
> >>>
> >>> diff --git a/arch/powerpc/kvm/e500_mmu_host.c
> >>> b/arch/powerpc/kvm/e500_mmu_host.c
> >>> index 1c6a9d7..089c227 100644
> >>> --- a/arch/powerpc/kvm/e500_mmu_host.c
> >>> +++ b/arch/powerpc/kvm/e500_mmu_host.c
> >>> @@ -64,13 +64,20 @@ 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 (!pfn_valid(pfn)) {
> >>
> >> Why not directly use kvm_is_mmio_pfn()?
> >
> > What I understand from this function (someone can correct me) is that it
> returns "false" when the page is managed by kernel and is not marked as RESERVED
> (for some reason). For us it does not matter whether the page is reserved or
> not, if it is kernel visible page then it is DDR.
> >
> 
> I think you are setting I|G by addressing all mmio pages, right? If so,
> 
>      KVM: direct mmio pfn check
> 
>      Userspace may specify memory slots that are backed by mmio pages rather
> than
>      normal RAM.  In some cases it is not enough to identify these mmio pages
>      by pfn_valid().  This patch adds checking the PageReserved as well.

Do you know what are those "some cases" and how checking PageReserved helps in those cases?

-Bharat

> 
> Tiejun
> 
> > -Bharat
> >
> >>
> >> Tiejun
> >>
> >>> +		mas2_attr |= MAS2_I | MAS2_G;
> >>> +	} else {
> >>>    #ifdef CONFIG_SMP
> >>> -	return (mas2 & MAS2_ATTRIB_MASK) | MAS2_M;
> >>> -#else
> >>> -	return mas2 & MAS2_ATTRIB_MASK;
> >>> +		mas2_attr |= MAS2_M;
> >>>    #endif
> >>> +	}
> >>> +	return mas2_attr;
> >>>    }
> >>>
> >>>    /*
> >>> @@ -313,7 +320,7 @@ 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);
> >>>
> >>>
> >>
> >
> 
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