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

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

On Tue, 16 Jun 2015 18:53:51 +1000
Alexey Kardashevskiy <aik@ozlabs.ru> 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.

> 
> > 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 <gkurz@linux.vnet.ibm.com>
> > ---
> >   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;
> >       }
> >
> >
> >
> 
>