Re: [PATCH 1/4] iommu/vt-d: Disable superpage for Geminilake igfx

[Lu Baolu <baolu.lu@linux.intel.com>]

On 7/12/21 11:47 PM, Ville Syrjälä wrote:
> On Mon, Jul 12, 2021 at 07:23:07AM +0800, Lu Baolu wrote:
>> On 7/10/21 12:47 AM, Ville Syrjala wrote:
>>> From: Ville Syrjälä<ville.syrjala@linux.intel.com>
>>>
>>> While running "gem_exec_big --r single" from igt-gpu-tools on
>>> Geminilake as soon as a 2M mapping is made I tend to get a DMAR
>>> write fault. Strangely the faulting address is always a 4K page
>>> and usually very far away from the 2M page that got mapped.
>>> But if no 2M mappings get used I can't reproduce the fault.
>>>
>>> I also tried to dump the PTE for the faulting address but it actually
>>> looks correct to me (ie. definitely seems to have the write bit set):
>>>    DMAR: DRHD: handling fault status reg 2
>>>    DMAR: [DMA Write] Request device [00:02.0] PASID ffffffff fault addr 7fa8a78000 [fault reason 05] PTE Write access is not set
>>>    DMAR: fault 7fa8a78000 (level=1) PTE = 149efc003
>>>
>>> So not really sure what's going on and this might just be full on duct
>>> tape, but it seems to work here. The machine has now survived a whole day
>>> running that test whereas with superpage enabled it fails in less than
>>> a minute usually.
>>>
>>> TODO: might be nice to disable superpage only for the igfx iommu
>>>         instead of both iommus
>> If all these quirks are about igfx dedicated iommu's, I would suggest to
>> disable superpage only for the igfx ones.
> Sure. Unfortunately there's no convenient mechanism to do that in
> the iommu driver that I can immediately see. So not something I
> can just whip up easily. Since you're actually familiar with the
> driver maybe you can come up with a decent solution for that?
> 

How about something like below? [no compile, no test...]

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 1131b8efb050..2d51ef288a9e 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -338,6 +338,7 @@ static int intel_iommu_strict;
  static int intel_iommu_superpage = 1;
  static int iommu_identity_mapping;
  static int iommu_skip_te_disable;
+static int iommu_skip_igfx_superpage;

  #define IDENTMAP_GFX		2
  #define IDENTMAP_AZALIA		4
@@ -652,6 +653,27 @@ static bool domain_update_iommu_snooping(struct 
intel_iommu *skip)
  	return ret;
  }

+static bool domain_use_super_page(struct dmar_domain *domain)
+{
+	struct dmar_drhd_unit *drhd;
+	struct intel_iommu *iommu;
+	bool ret = true;
+
+	if (!intel_iommu_superpage)
+		return false;
+
+	rcu_read_lock();
+	for_each_active_iommu(iommu, drhd) {
+		if (drhd->gfx_dedicated && iommu_skip_igfx_superpage) {
+			ret = false;
+			break
+		}
+	}
+	rcu_read_unlock();
+
+	return ret;
+}
+
  static int domain_update_iommu_superpage(struct dmar_domain *domain,
  					 struct intel_iommu *skip)
  {
@@ -659,7 +681,7 @@ static int domain_update_iommu_superpage(struct 
dmar_domain *domain,
  	struct intel_iommu *iommu;
  	int mask = 0x3;

-	if (!intel_iommu_superpage)
+	if (!domain_use_super_page(domain))
  		return 0;

  	/* set iommu_superpage to the smallest common denominator */
@@ -5656,6 +5678,14 @@ DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 
0x1632, quirk_iommu_igfx);
  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x163A, quirk_iommu_igfx);
  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x163D, quirk_iommu_igfx);

+static void quirk_skip_igfx_superpage(struct pci_dev *dev)
+{
+	pci_info(dev, "Disabling IOMMU superpage for graphics on this chipset\n");
+	iommu_skip_igfx_superpage = 1;
+}
+
+DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_INTEL, 0x3184, 
quirk_skip_igfx_superpage);
+
  static void quirk_iommu_rwbf(struct pci_dev *dev)
  {
  	if (risky_device(dev))

Best regards,
baolu
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