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

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

> -----Original Message-----
> From: "“tiejun.chen”" [mailto:tiejun.chen@windriver.com]
> Sent: Thursday, July 18, 2013 1:52 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 04:08 PM, Bhushan Bharat-R65777 wrote:
> >
> >
> >> -----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?
> 
> No, myself didn't see these actual cases in qemu,too. But this should be
> chronically persistent as I understand ;-)

Then I will wait till someone educate me :)

-Bharat

> 
> Tiejun
> 
> >
> > -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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