Re: [PATCH v5 7/8] iommu/arm-smmu: Get associated RMR info and install bypass SMR

[Jon Nettleton <jon@solid-run.com>]

On Mon, Jun 14, 2021 at 6:51 PM Shameerali Kolothum Thodi
<shameerali.kolothum.thodi@huawei.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Robin Murphy [mailto:robin.murphy@arm.com]
> > Sent: 14 June 2021 11:06
> > To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>;
> > linux-arm-kernel@lists.infradead.org; linux-acpi@vger.kernel.org;
> > iommu@lists.linux-foundation.org
> > Cc: jon@solid-run.com; Linuxarm <linuxarm@huawei.com>;
> > steven.price@arm.com; Guohanjun (Hanjun Guo) <guohanjun@huawei.com>;
> > yangyicong <yangyicong@huawei.com>; Sami.Mujawar@arm.com;
> > wanghuiqiang <wanghuiqiang@huawei.com>
> > Subject: Re: [PATCH v5 7/8] iommu/arm-smmu: Get associated RMR info and
> > install bypass SMR
> >
> > On 2021-05-24 12:02, Shameer Kolothum wrote:
> > > From: Jon Nettleton <jon@solid-run.com>
> > >
> > > Check if there is any RMR info associated with the devices behind
> > > the SMMU and if any, install bypass SMRs for them. This is to
> > > keep any ongoing traffic associated with these devices alive
> > > when we enable/reset SMMU during probe().
> > >
> > > Signed-off-by: Jon Nettleton <jon@solid-run.com>
> > > Signed-off-by: Steven Price <steven.price@arm.com>
> > > Signed-off-by: Shameer Kolothum
> > <shameerali.kolothum.thodi@huawei.com>
> > > ---
> > >   drivers/iommu/arm/arm-smmu/arm-smmu.c | 65
> > +++++++++++++++++++++++++++
> > >   1 file changed, 65 insertions(+)
> > >
> > > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > > index 6f72c4d208ca..56db3d3238fc 100644
> > > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > > @@ -2042,6 +2042,67 @@ err_reset_platform_ops: __maybe_unused;
> > >     return err;
> > >   }
> > >
> > > +static void arm_smmu_rmr_install_bypass_smr(struct arm_smmu_device
> > *smmu)
> > > +{
> > > +   struct list_head rmr_list;
> > > +   struct iommu_resv_region *e;
> > > +   int i, cnt = 0;
> > > +   u32 smr;
> > > +   u32 reg;
> > > +
> > > +   INIT_LIST_HEAD(&rmr_list);
> > > +   if (iommu_dma_get_rmrs(dev_fwnode(smmu->dev), &rmr_list))
> > > +           return;
> > > +
> > > +   reg = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_sCR0);
> > > +
> > > +   if ((reg & ARM_SMMU_sCR0_USFCFG) && !(reg &
> > ARM_SMMU_sCR0_CLIENTPD)) {
> > > +           /*
> > > +            * SMMU is already enabled and disallowing bypass, so preserve
> > > +            * the existing SMRs
> > > +            */
> > > +           for (i = 0; i < smmu->num_mapping_groups; i++) {
> > > +                   smr = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_SMR(i));
> >
> > To reiterate, just because a bootloader/crashed kernel/whatever may have
> > left some configuration behind doesn't mean that it matters (e.g. what
> > if these SMRs are pointing at translation contexts?). All we should be
> > doing here is setting the relevant RMR accommodations in our "clean
> > slate" software state before the reset routine applies it to the
> > hardware, just like patch #5 does for SMMUv3.
> >
> > Trying to safely reset an SMMU when we discover it with CLIENTPD=0 is
> > really another issue entirely, and I'd say is beyond the scope of this
> > series
> >
> > > +                   if (!FIELD_GET(ARM_SMMU_SMR_VALID, smr))
> > > +                           continue;
> >
> > Note that that's not even necessarily correct (thanks to EXIDS).
> >
> > > +                   smmu->smrs[i].id = FIELD_GET(ARM_SMMU_SMR_ID, smr);
> > > +                   smmu->smrs[i].mask = FIELD_GET(ARM_SMMU_SMR_MASK,
> > smr);
> > > +                   smmu->smrs[i].valid = true;
> > > +           }
> > > +   }
> > > +
> > > +   list_for_each_entry(e, &rmr_list, list) {
> > > +           u32 sid = e->fw_data.rmr.sid;
> > > +
> > > +           i = arm_smmu_find_sme(smmu, sid, ~0);
> > > +           if (i < 0)
> > > +                   continue;
> > > +           if (smmu->s2crs[i].count == 0) {
> > > +                   smmu->smrs[i].id = sid;
> > > +                   smmu->smrs[i].mask = ~0;
> >
> > This is very wrong (as has now already been pointed out).
> >
> > > +                   smmu->smrs[i].valid = true;
> > > +           }
> > > +           smmu->s2crs[i].count++;
> > > +           smmu->s2crs[i].type = S2CR_TYPE_BYPASS;
> > > +           smmu->s2crs[i].privcfg = S2CR_PRIVCFG_DEFAULT;
> > > +           smmu->s2crs[i].cbndx = 0xff;
> >
> > Nit: cbndx is left uninitialised for bypass/fault entries elsewhere, so
> > there's little point touching it here.
> >
> > > +
> > > +           cnt++;
> > > +   }
> > > +
> > > +   if ((reg & ARM_SMMU_sCR0_USFCFG) && !(reg &
> > ARM_SMMU_sCR0_CLIENTPD)) {
> > > +           /* Remove the valid bit for unused SMRs */
> > > +           for (i = 0; i < smmu->num_mapping_groups; i++) {
> > > +                   if (smmu->s2crs[i].count == 0)
> > > +                           smmu->smrs[i].valid = false;
> > > +           }
> >
> > If this dance is only about avoiding stream match conflicts when trying
> > to reprogram live SMRs, simply turning the SMMU off beforehand would be
> > a lot simpler.
>
> Hi Steve/Jon,
>
> Since I don’t have access to an SMMUv2 setup, really appreciate if one of you
> could please take a look at the above comments and provide me with a tested
> code so that I can include it in the v6 that I am planning to send out soon.

Will do.  Thanks.
Jon

>
> Thanks,
> Shameer
>
> > Robin.
> >
> > > +   }
> > > +
> > > +   dev_notice(smmu->dev, "\tpreserved %d boot mapping%s\n", cnt,
> > > +              cnt == 1 ? "" : "s");
> > > +   iommu_dma_put_rmrs(dev_fwnode(smmu->dev), &rmr_list);
> > > +}
> > > +
> > >   static int arm_smmu_device_probe(struct platform_device *pdev)
> > >   {
> > >     struct resource *res;
> > > @@ -2168,6 +2229,10 @@ static int arm_smmu_device_probe(struct
> > platform_device *pdev)
> > >     }
> > >
> > >     platform_set_drvdata(pdev, smmu);
> > > +
> > > +   /* Check for RMRs and install bypass SMRs if any */
> > > +   arm_smmu_rmr_install_bypass_smr(smmu);
> > > +
> > >     arm_smmu_device_reset(smmu);
> > >     arm_smmu_test_smr_masks(smmu);
> > >
> > >