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

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

> -----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. 

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);
> >
> >
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