[PATCH v3 0/4] iommu/vt-d: Force snooping improvement

[PATCH v3 0/4] iommu/vt-d: Force snooping improvement

[Lu Baolu]

Hi folks,

Previously, the IOMMU capability of enforcing cache coherency was queried
through iommu_capable(IOMMU_CAP_CACHE_COHERENCY). This is a global
capability, hence the IOMMU driver reports support for this capability
only when all IOMMUs in the system has this support.

Commit 6043257b1de06 ("iommu: Introduce the domain op
enforce_cache_coherency()") converts this into a per-domain test-and-set
option, and the previous iommu_capable(IOMMU_CAP_CACHE_COHERENCY) is
deprecated.

This is a follow-up series which improves the Intel IOMMU driver to
support the per-domain scheme better.

Best regards,
baolu

Change log:
v3:
 - Hold the device_domain_lock when check and set force snooping.
 - Refind the commit messages.

v2:
 - https://lore.kernel.org/linux-iommu/20220505010710.1477739-1-baolu.lu@linux.intel.com/
 - Check whether force_snooping has already been set in
   intel_iommu_enforce_cache_coherency().
 - Set PGSNP pasid bit field during domain attaching if forcing_snooping
   is set.
 - Remove redundant list_empty() checks.
 - Add dmar_domain->set_pte_snp and set it if force snooping is enforced
   on a domain with 2nd-level translation.

v1:
 - https://lore.kernel.org/linux-iommu/20220501112434.874236-1-baolu.lu@linux.intel.com
 - Initial post.

Lu Baolu (4):
  iommu/vt-d: Block force-snoop domain attaching if no SC support
  iommu/vt-d: Check domain force_snooping against attached devices
  iommu/vt-d: Remove domain_update_iommu_snooping()
  iommu/vt-d: Remove hard coding PGSNP bit in PASID entries

 include/linux/intel-iommu.h |  1 +
 drivers/iommu/intel/pasid.h |  2 +
 drivers/iommu/intel/iommu.c | 90 ++++++++++++++++++++++---------------
 drivers/iommu/intel/pasid.c | 26 +++++++++--
 4 files changed, 80 insertions(+), 39 deletions(-)

-- 
2.25.1

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[PATCH v3 1/4] iommu/vt-d: Block force-snoop domain attaching if no SC support

[Lu Baolu]

In the attach_dev callback of the default domain ops, if the domain has
been set force_snooping, but the iommu hardware of the device does not
support SC(Snoop Control) capability, the callback should block it and
return a corresponding error code.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
---
 drivers/iommu/intel/iommu.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 2990f80c5e08..b4802f4055a0 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4367,6 +4367,9 @@ static int prepare_domain_attach_device(struct iommu_domain *domain,
 	if (!iommu)
 		return -ENODEV;
 
+	if (dmar_domain->force_snooping && !ecap_sc_support(iommu->ecap))
+		return -EOPNOTSUPP;
+
 	/* check if this iommu agaw is sufficient for max mapped address */
 	addr_width = agaw_to_width(iommu->agaw);
 	if (addr_width > cap_mgaw(iommu->cap))
-- 
2.25.1

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[PATCH v3 2/4] iommu/vt-d: Check domain force_snooping against attached devices

[Lu Baolu]

As domain->force_snooping only impacts the devices attached with the
domain, there's no need to check against all IOMMU units. On the other
hand, force_snooping could be set on a domain no matter whether it has
been attached or not, and once set it is an immutable flag. If no
device attached, the operation always succeeds. Then this empty domain
can be only attached to a device of which the IOMMU supports snoop
control.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 include/linux/intel-iommu.h |  1 +
 drivers/iommu/intel/pasid.h |  2 ++
 drivers/iommu/intel/iommu.c | 53 ++++++++++++++++++++++++++++++++++---
 drivers/iommu/intel/pasid.c | 23 ++++++++++++++++
 4 files changed, 76 insertions(+), 3 deletions(-)

diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
index 72e5d7900e71..4f29139bbfc3 100644
--- a/include/linux/intel-iommu.h
+++ b/include/linux/intel-iommu.h
@@ -540,6 +540,7 @@ struct dmar_domain {
 	u8 has_iotlb_device: 1;
 	u8 iommu_coherency: 1;		/* indicate coherency of iommu access */
 	u8 force_snooping : 1;		/* Create IOPTEs with snoop control */
+	u8 set_pte_snp:1;
 
 	struct list_head devices;	/* all devices' list */
 	struct iova_domain iovad;	/* iova's that belong to this domain */
diff --git a/drivers/iommu/intel/pasid.h b/drivers/iommu/intel/pasid.h
index ab4408c824a5..583ea67fc783 100644
--- a/drivers/iommu/intel/pasid.h
+++ b/drivers/iommu/intel/pasid.h
@@ -123,4 +123,6 @@ void intel_pasid_tear_down_entry(struct intel_iommu *iommu,
 				 bool fault_ignore);
 int vcmd_alloc_pasid(struct intel_iommu *iommu, u32 *pasid);
 void vcmd_free_pasid(struct intel_iommu *iommu, u32 pasid);
+void intel_pasid_setup_page_snoop_control(struct intel_iommu *iommu,
+					  struct device *dev, u32 pasid);
 #endif /* __INTEL_PASID_H */
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index b4802f4055a0..048ebfbd5fcb 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2459,7 +2459,7 @@ static int domain_setup_first_level(struct intel_iommu *iommu,
 	if (level == 5)
 		flags |= PASID_FLAG_FL5LP;
 
-	if (domain->domain.type == IOMMU_DOMAIN_UNMANAGED)
+	if (domain->force_snooping)
 		flags |= PASID_FLAG_PAGE_SNOOP;
 
 	return intel_pasid_setup_first_level(iommu, dev, (pgd_t *)pgd, pasid,
@@ -4444,7 +4444,7 @@ static int intel_iommu_map(struct iommu_domain *domain,
 		prot |= DMA_PTE_READ;
 	if (iommu_prot & IOMMU_WRITE)
 		prot |= DMA_PTE_WRITE;
-	if (dmar_domain->force_snooping)
+	if (dmar_domain->set_pte_snp)
 		prot |= DMA_PTE_SNP;
 
 	max_addr = iova + size;
@@ -4567,13 +4567,60 @@ static phys_addr_t intel_iommu_iova_to_phys(struct iommu_domain *domain,
 	return phys;
 }
 
+static bool domain_support_force_snooping(struct dmar_domain *domain)
+{
+	struct device_domain_info *info;
+	bool support = true;
+
+	assert_spin_locked(&device_domain_lock);
+	list_for_each_entry(info, &domain->devices, link) {
+		if (!ecap_sc_support(info->iommu->ecap)) {
+			support = false;
+			break;
+		}
+	}
+
+	return support;
+}
+
+static void domain_set_force_snooping(struct dmar_domain *domain)
+{
+	struct device_domain_info *info;
+
+	assert_spin_locked(&device_domain_lock);
+
+	/*
+	 * Second level page table supports per-PTE snoop control. The
+	 * iommu_map() interface will handle this by setting SNP bit.
+	 */
+	if (!domain_use_first_level(domain)) {
+		domain->set_pte_snp = true;
+		return;
+	}
+
+	list_for_each_entry(info, &domain->devices, link)
+		intel_pasid_setup_page_snoop_control(info->iommu, info->dev,
+						     PASID_RID2PASID);
+}
+
 static bool intel_iommu_enforce_cache_coherency(struct iommu_domain *domain)
 {
 	struct dmar_domain *dmar_domain = to_dmar_domain(domain);
+	unsigned long flags;
 
-	if (!domain_update_iommu_snooping(NULL))
+	if (dmar_domain->force_snooping)
+		return true;
+
+	spin_lock_irqsave(&device_domain_lock, flags);
+	if (!domain_support_force_snooping(dmar_domain)) {
+		spin_unlock_irqrestore(&device_domain_lock, flags);
 		return false;
+	}
+
+	domain_set_force_snooping(dmar_domain);
 	dmar_domain->force_snooping = true;
+	spin_unlock_irqrestore(&device_domain_lock, flags);
+
 	return true;
 }
 
diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
index f8d215d85695..41a0e3b02c79 100644
--- a/drivers/iommu/intel/pasid.c
+++ b/drivers/iommu/intel/pasid.c
@@ -762,3 +762,26 @@ int intel_pasid_setup_pass_through(struct intel_iommu *iommu,
 
 	return 0;
 }
+
+/*
+ * Set the page snoop control for a pasid entry which has been set up.
+ */
+void intel_pasid_setup_page_snoop_control(struct intel_iommu *iommu,
+					  struct device *dev, u32 pasid)
+{
+	struct pasid_entry *pte;
+	u16 did;
+
+	spin_lock(&iommu->lock);
+	pte = intel_pasid_get_entry(dev, pasid);
+	if (WARN_ON(!pte || !pasid_pte_is_present(pte))) {
+		spin_unlock(&iommu->lock);
+		return;
+	}
+
+	pasid_set_pgsnp(pte);
+	did = pasid_get_domain_id(pte);
+	spin_unlock(&iommu->lock);
+
+	pasid_flush_caches(iommu, pte, pasid, did);
+}
-- 
2.25.1

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RE: [PATCH v3 2/4] iommu/vt-d: Check domain force_snooping against attached devices

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Friday, May 6, 2022 1:27 PM
> +
> +/*
> + * Set the page snoop control for a pasid entry which has been set up.
> + */
> +void intel_pasid_setup_page_snoop_control(struct intel_iommu *iommu,
> +					  struct device *dev, u32 pasid)
> +{
> +	struct pasid_entry *pte;
> +	u16 did;
> +
> +	spin_lock(&iommu->lock);
> +	pte = intel_pasid_get_entry(dev, pasid);
> +	if (WARN_ON(!pte || !pasid_pte_is_present(pte))) {
> +		spin_unlock(&iommu->lock);
> +		return;
> +	}
> +
> +	pasid_set_pgsnp(pte);
> +	did = pasid_get_domain_id(pte);
> +	spin_unlock(&iommu->lock);
> +
> +	pasid_flush_caches(iommu, pte, pasid, did);
> +}

The comment of pasid_flush_caches() says:

/*
 * This function flushes cache for a newly setup pasid table entry.
 * Caller of it should not modify the in-use pasid table entries.
 */

Can you check whether that comment still hold?
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Re: [PATCH v3 2/4] iommu/vt-d: Check domain force_snooping against attached devices

[Baolu Lu]

On 2022/5/6 14:10, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Friday, May 6, 2022 1:27 PM
>> +
>> +/*
>> + * Set the page snoop control for a pasid entry which has been set up.
>> + */
>> +void intel_pasid_setup_page_snoop_control(struct intel_iommu *iommu,
>> +					  struct device *dev, u32 pasid)
>> +{
>> +	struct pasid_entry *pte;
>> +	u16 did;
>> +
>> +	spin_lock(&iommu->lock);
>> +	pte = intel_pasid_get_entry(dev, pasid);
>> +	if (WARN_ON(!pte || !pasid_pte_is_present(pte))) {
>> +		spin_unlock(&iommu->lock);
>> +		return;
>> +	}
>> +
>> +	pasid_set_pgsnp(pte);
>> +	did = pasid_get_domain_id(pte);
>> +	spin_unlock(&iommu->lock);
>> +
>> +	pasid_flush_caches(iommu, pte, pasid, did);
>> +}
> 
> The comment of pasid_flush_caches() says:
> 
> /*
>   * This function flushes cache for a newly setup pasid table entry.
>   * Caller of it should not modify the in-use pasid table entries.
>   */
> 
> Can you check whether that comment still hold?

I am sorry that I overlooked this. Very appreciated for pointing this
out!

How about below additional changes?

diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
index da47406011d3..68f7e8cfa848 100644
--- a/drivers/iommu/intel/pasid.c
+++ b/drivers/iommu/intel/pasid.c
@@ -782,5 +782,24 @@ void intel_pasid_setup_page_snoop_control(struct 
intel_iommu *iommu,
         did = pasid_get_domain_id(pte);
         spin_unlock(&iommu->lock);

-       pasid_flush_caches(iommu, pte, pasid, did);
+       if (!ecap_coherent(iommu->ecap))
+               clflush_cache_range(pte, sizeof(*pte));
+
+       /*
+        * VT-d spec 3.4 table23 states guides for cache invalidation:
+        *
+        * - PASID-selective-within-Domain PASID-cache invalidation
+        * - PASID-selective PASID-based IOTLB invalidation
+        * - If (pasid is RID_PASID)
+        *    - Global Device-TLB invalidation to affected functions
+        *   Else
+        *    - PASID-based Device-TLB invalidation (with S=1 and
+        *      Addr[63:12]=0x7FFFFFFF_FFFFF) to affected functions
+        */
+       pasid_cache_invalidation_with_pasid(iommu, did, pasid);
+       qi_flush_piotlb(iommu, did, pasid, 0, -1, 0);
+
+       /* Device IOTLB doesn't need to be flushed in caching mode. */
+       if (!cap_caching_mode(iommu->cap))
+               devtlb_invalidation_with_pasid(iommu, dev, pasid);
  }

Best regards,
baolu
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[PATCH v3 3/4] iommu/vt-d: Remove domain_update_iommu_snooping()

[Lu Baolu]

The IOMMU force snooping capability is not required to be consistent
among all the IOMMUs anymore. Remove force snooping capability check
in the IOMMU hot-add path and domain_update_iommu_snooping() becomes
a dead code now.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
---
 drivers/iommu/intel/iommu.c | 34 +---------------------------------
 1 file changed, 1 insertion(+), 33 deletions(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 048ebfbd5fcb..444d51a18c93 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -533,33 +533,6 @@ static void domain_update_iommu_coherency(struct dmar_domain *domain)
 	rcu_read_unlock();
 }
 
-static bool domain_update_iommu_snooping(struct intel_iommu *skip)
-{
-	struct dmar_drhd_unit *drhd;
-	struct intel_iommu *iommu;
-	bool ret = true;
-
-	rcu_read_lock();
-	for_each_active_iommu(iommu, drhd) {
-		if (iommu != skip) {
-			/*
-			 * If the hardware is operating in the scalable mode,
-			 * the snooping control is always supported since we
-			 * always set PASID-table-entry.PGSNP bit if the domain
-			 * is managed outside (UNMANAGED).
-			 */
-			if (!sm_supported(iommu) &&
-			    !ecap_sc_support(iommu->ecap)) {
-				ret = false;
-				break;
-			}
-		}
-	}
-	rcu_read_unlock();
-
-	return ret;
-}
-
 static int domain_update_iommu_superpage(struct dmar_domain *domain,
 					 struct intel_iommu *skip)
 {
@@ -3606,12 +3579,7 @@ static int intel_iommu_add(struct dmar_drhd_unit *dmaru)
 			iommu->name);
 		return -ENXIO;
 	}
-	if (!ecap_sc_support(iommu->ecap) &&
-	    domain_update_iommu_snooping(iommu)) {
-		pr_warn("%s: Doesn't support snooping.\n",
-			iommu->name);
-		return -ENXIO;
-	}
+
 	sp = domain_update_iommu_superpage(NULL, iommu) - 1;
 	if (sp >= 0 && !(cap_super_page_val(iommu->cap) & (1 << sp))) {
 		pr_warn("%s: Doesn't support large page.\n",
-- 
2.25.1

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[PATCH v3 4/4] iommu/vt-d: Remove hard coding PGSNP bit in PASID entries

[Lu Baolu]

As enforce_cache_coherency has been introduced into the iommu_domain_ops,
the kernel component which owns the iommu domain is able to opt-in its
requirement for force snooping support. The iommu driver has no need to
hard code the page snoop control bit in the PASID table entries anymore.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
---
 drivers/iommu/intel/pasid.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/drivers/iommu/intel/pasid.c b/drivers/iommu/intel/pasid.c
index 41a0e3b02c79..0abfa7fc7fb0 100644
--- a/drivers/iommu/intel/pasid.c
+++ b/drivers/iommu/intel/pasid.c
@@ -710,9 +710,6 @@ int intel_pasid_setup_second_level(struct intel_iommu *iommu,
 	pasid_set_fault_enable(pte);
 	pasid_set_page_snoop(pte, !!ecap_smpwc(iommu->ecap));
 
-	if (domain->domain.type == IOMMU_DOMAIN_UNMANAGED)
-		pasid_set_pgsnp(pte);
-
 	/*
 	 * Since it is a second level only translation setup, we should
 	 * set SRE bit as well (addresses are expected to be GPAs).
-- 
2.25.1

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