Re: [Qemu-devel] [Qemu-ppc] [PATCH] spapr_iommu: fix erroneous sanity check in h_put_tce_indirect()

[Alexey Kardashevskiy]

On 06/16/2015 07:24 PM, Greg Kurz wrote:
> On Tue, 16 Jun 2015 18:53:51 +1000
> Alexey Kardashevskiy <address@hidden> wrote:
>
> > On 06/16/2015 03:28 AM, Greg Kurz wrote:
> > > According to PAPR+ 3.2.2.2, the TCE is implemented as follows:
> > >         bits  0-51: real page number
> > >         bits 52-61: reserved for future use
> > >         bits 62-63: page protection (read-only, write-only, read-write)
> >
> >
> >
> > tce_list is not a TCE, it is "The logical address of a page of (4 K long on
> > a 4 K boundary) of TCE contents to be stored in the TCE table (contains
> > logical address of storage page to be mapped)" so we rather want to remove
> > (tce_list & ~SPAPR_TCE_RW) below.
>
> Oops my bad for the confustion... :-\
>
> Then it looks like SPAPR_TCE_RW can be dropped as well since put_tce_emu() uses
> IOMMU_RW instead.


Well, spapr_tce_translate_iommu() should actually translate SPAPR_TCE_xxx 
(PAPR defined flags) to IOMMU_xxx (QEMU IOMMUTLBEntry permission bits), not 
just rely on the fact that they match.


> > > Possible values for the protection bits are necessarly non-zero and thus
> > > H_PUT_TCE_INDIRECT currently always fails and returns H_PARAMETER.
> > >
> > > The code explicitly clears the protection bits when computing the TCE offset,
> > > a few lines below (tce_list & ~SPAPR_TCE_RW)... The sanity check is obviously
> > > wrong for these bits.
> > >
> > > Moreover, I could find no indication in PAPR+ that using the other reserved
> > > bits should error out with H_PARAMETER.
> > >
> > > This patch simply drops the offending check.
> > >
> > > Signed-off-by: Greg Kurz <address@hidden>
> > > ---
> > >    hw/ppc/spapr_iommu.c |    2 +-
> > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/hw/ppc/spapr_iommu.c b/hw/ppc/spapr_iommu.c
> > > index 8cd9dba9ac4d..37a1110c9d87 100644
> > > --- a/hw/ppc/spapr_iommu.c
> > > +++ b/hw/ppc/spapr_iommu.c
> > > @@ -258,7 +258,7 @@ static target_ulong h_put_tce_indirect(PowerPCCPU *cpu,
> > >            return H_PARAMETER;
> > >        }
> > >
> > > -    if ((npages > 512) || (tce_list & SPAPR_TCE_PAGE_MASK)) {
> > > +    if (npages > 512) {
> > >            return H_PARAMETER;
> > >        }


--
Alexey