Re: [RFC 2/2] iommu: arm-smmu: Don't blindly use first SMR to calculate mask

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Wed 12 Jun 10:58 PDT 2019, Jeffrey Hugo wrote:

> On Wed, Jun 5, 2019 at 3:09 PM Bjorn Andersson
> <bjorn.andersson@linaro.org> wrote:
> >
> > With the SMRs inherited from the bootloader the first SMR might actually
> > be valid and in use. As such probing the SMR mask using the first SMR
> > might break a stream in use. Search for an unused stream and use this to
> > probe the SMR mask.
> >
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
> 
> Reviewed-by: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
> 
> I don't quite like the situation where the is no SMR to compute the mask, but I
> think the way you've handled it is the best option/
> 

Right, if this happens we would end up using the smr_mask that was
previously calculated. We just won't update it based on the hardware.

> I'm curious, why is this not included in patch #1?  Seems like patch
> #1 introduces
> the issue, yet doesn't also fix it.
> 

You're right, didn't think about that. This needs to either predate that
patch or be included in it.

Thanks,
Bjorn

> > ---
> >  drivers/iommu/arm-smmu.c | 20 ++++++++++++++++----
> >  1 file changed, 16 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> > index c8629a656b42..0c6f5fe6f382 100644
> > --- a/drivers/iommu/arm-smmu.c
> > +++ b/drivers/iommu/arm-smmu.c
> > @@ -1084,23 +1084,35 @@ static void arm_smmu_test_smr_masks(struct arm_smmu_device *smmu)
> >  {
> >         void __iomem *gr0_base = ARM_SMMU_GR0(smmu);
> >         u32 smr;
> > +       int idx;
> >
> >         if (!smmu->smrs)
> >                 return;
> >
> > +       for (idx = 0; idx < smmu->num_mapping_groups; idx++) {
> > +               smr = readl_relaxed(gr0_base + ARM_SMMU_GR0_SMR(idx));
> > +               if (!(smr & SMR_VALID))
> > +                       break;
> > +       }
> > +
> > +       if (idx == smmu->num_mapping_groups) {
> > +               dev_err(smmu->dev, "Unable to compute streamid_mask\n");
> > +               return;
> > +       }
> > +
> >         /*
> >          * SMR.ID bits may not be preserved if the corresponding MASK
> >          * bits are set, so check each one separately. We can reject
> >          * masters later if they try to claim IDs outside these masks.
> >          */
> >         smr = smmu->streamid_mask << SMR_ID_SHIFT;
> > -       writel_relaxed(smr, gr0_base + ARM_SMMU_GR0_SMR(0));
> > -       smr = readl_relaxed(gr0_base + ARM_SMMU_GR0_SMR(0));
> > +       writel_relaxed(smr, gr0_base + ARM_SMMU_GR0_SMR(idx));
> > +       smr = readl_relaxed(gr0_base + ARM_SMMU_GR0_SMR(idx));
> >         smmu->streamid_mask = smr >> SMR_ID_SHIFT;
> >
> >         smr = smmu->streamid_mask << SMR_MASK_SHIFT;
> > -       writel_relaxed(smr, gr0_base + ARM_SMMU_GR0_SMR(0));
> > -       smr = readl_relaxed(gr0_base + ARM_SMMU_GR0_SMR(0));
> > +       writel_relaxed(smr, gr0_base + ARM_SMMU_GR0_SMR(idx));
> > +       smr = readl_relaxed(gr0_base + ARM_SMMU_GR0_SMR(idx));
> >         smmu->smr_mask_mask = smr >> SMR_MASK_SHIFT;
> >  }
> >
> > --
> > 2.18.0
> >
> >
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