[PATCH v2 06/12] VT-d: respect ACPI SATC's ATC_REQUIRED flag

[Jan Beulich <jbeulich@xxxxxxxx>]

When the flag is set, permit Dom0 to control the device (no worse than
what we had before and in line with other "best effort" behavior we use
when it comes to Dom0), but suppress passing through to DomU-s unless
ATS can actually be enabled for such devices (and was explicitly enabled
on the command line).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Re-base over new earlier patches.

--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -225,7 +225,11 @@ exceptions (watchdog NMIs and unexpected
 > Default: `false`
 
 Permits Xen to set up and use PCI Address Translation Services.  This is a
-performance optimisation for PCI Passthrough.
+performance optimisation for PCI Passthrough.  Note that firmware may indicate
+that certain devices need to have ATS enabled for proper operation. For such
+devices ATS will be enabled by default, unless the option is used in its
+negative form.  Such devices will still not be eligible for passing through to
+guests, unless the option is used in its positive form.
 
 **WARNING: Xen cannot currently safely use ATS because of its synchronous wait
 loops for Queued Invalidation completions.**
--- a/xen/drivers/passthrough/vtd/dmar.c
+++ b/xen/drivers/passthrough/vtd/dmar.c
@@ -253,6 +253,24 @@ struct acpi_atsr_unit *acpi_find_matched
     return all_ports;
 }
 
+const struct acpi_satc_unit *acpi_find_matched_satc_unit(
+    const struct pci_dev *pdev)
+{
+    const struct acpi_satc_unit *satc;
+
+    list_for_each_entry ( satc, &acpi_satc_units, list )
+    {
+        if ( satc->segment != pdev->seg )
+            continue;
+
+        for ( unsigned int i = 0; i < satc->scope.devices_cnt; ++i )
+            if ( satc->scope.devices[i] == pdev->sbdf.bdf )
+                return satc;
+    }
+
+    return NULL;
+}
+
 struct acpi_rhsa_unit *drhd_to_rhsa(const struct acpi_drhd_unit *drhd)
 {
     struct acpi_rhsa_unit *rhsa;
--- a/xen/drivers/passthrough/vtd/dmar.h
+++ b/xen/drivers/passthrough/vtd/dmar.h
@@ -112,6 +112,8 @@ struct acpi_satc_unit {
 
 struct acpi_drhd_unit *acpi_find_matched_drhd_unit(const struct pci_dev *);
 struct acpi_atsr_unit *acpi_find_matched_atsr_unit(const struct pci_dev *);
+const struct acpi_satc_unit *acpi_find_matched_satc_unit(
+    const struct pci_dev *pdev);
 
 #define DMAR_TYPE 1
 #define RMRR_TYPE 2
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -2364,6 +2364,26 @@ static int cf_check intel_iommu_add_devi
     if ( ret )
         dprintk(XENLOG_ERR VTDPREFIX, "%pd: context mapping failed\n",
                 pdev->domain);
+    else if ( !pdev->broken )
+    {
+        const struct acpi_drhd_unit *drhd = acpi_find_matched_drhd_unit(pdev);
+        const struct acpi_satc_unit *satc = acpi_find_matched_satc_unit(pdev);
+
+        /*
+         * Prevent the device from getting assigned to an unprivileged domain
+         * when firmware indicates ATS is required, but ATS could not be 
enabled
+         * or was not explicitly enabled via command line option.
+         */
+        if ( satc && satc->atc_required &&
+             (!drhd || ats_device(pdev, drhd) <= 0 ||
+              !pci_ats_enabled(pdev->seg, pdev->bus, pdev->devfn) ||
+              opt_ats < 0) )
+        {
+            printk(XENLOG_WARNING "ATS: %pp is not eligible for 
pass-through\n",
+                   &pdev->sbdf);
+            pdev->broken = true;
+        }
+    }
 
     return ret;
 }
@@ -2375,12 +2395,26 @@ static int cf_check intel_iommu_enable_d
 
     pci_vtd_quirk(pdev);
 
-    if ( ret <= 0 )
-        return ret;
+    if ( ret <= 0 ||
+         (ret = enable_ats_device(pdev, &drhd->iommu->ats_devices)) < 0 ||
+         opt_ats < 0 )
+    {
+        const struct acpi_satc_unit *satc = acpi_find_matched_satc_unit(pdev);
+
+        /*
+         * Besides in error cases also prevent the device from getting assigned
+         * to an unprivileged domain when firmware indicates ATS is required,
+         * but ATS use was not explicitly enabled via command line option.
+         */
+        if ( satc && satc->atc_required && !pdev->broken )
+        {
+            printk(XENLOG_WARNING "ATS: %pp is not eligible for 
pass-through\n",
+                   &pdev->sbdf);
+            pdev->broken = true;
+        }
+    }
 
-    ret = enable_ats_device(pdev, &drhd->iommu->ats_devices);
-
-    return ret >= 0 ? 0 : ret;
+    return ret <= 0 ? ret : 0;
 }
 
 static int cf_check intel_iommu_remove_device(u8 devfn, struct pci_dev *pdev)
--- a/xen/drivers/passthrough/vtd/x86/ats.c
+++ b/xen/drivers/passthrough/vtd/x86/ats.c
@@ -45,8 +45,9 @@ int ats_device(const struct pci_dev *pde
 {
     struct acpi_drhd_unit *ats_drhd;
     unsigned int pos, expfl = 0;
+    const struct acpi_satc_unit *satc;
 
-    if ( opt_ats <= 0 || !iommu_qinval )
+    if ( !opt_ats || !iommu_qinval )
         return 0;
 
     if ( !ecap_queued_inval(drhd->iommu->ecap) ||
@@ -61,6 +62,10 @@ int ats_device(const struct pci_dev *pde
          !acpi_find_matched_atsr_unit(pdev) )
         return 0;
 
+    satc = acpi_find_matched_satc_unit(pdev);
+    if ( opt_ats < 0 && (!satc || !satc->atc_required) )
+        return 0;
+
     ats_drhd = find_ats_dev_drhd(drhd->iommu);
     pos = pci_find_ext_capability(pdev->sbdf, PCI_EXT_CAP_ID_ATS);