[PATCH 1/2] VT-d: generalize and correct "iommu=no-igfx" handling

[Jan Beulich <jbeulich@xxxxxxxx>]

Linux'es supposedly equivalent "intel_iommu=igfx_off" deals with any
graphics devices (not just Intel ones) while at the same time limiting
the effect to IOMMUs covering only graphics devices. Keying the decision
to leave translation disabled for an IOMMU to merely a magic SBDF tuple
was wrong in the first place - systems may very well have non-graphics
devices at 0000:00:02.0 (ordinary root ports commonly live there, for
example). Any use of igd_drhd_address (and hence is_igd_drhd()) needs
further qualification.

Introduce a new "graphics only" field in struct acpi_drhd_unit and set
it according to device scope parsing outcome. Replace the bad use of
is_igd_drhd() in iommu_enable_translation() by use of this new field.

While adding the new field also convert the adjacent include_all one to
"bool".

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
I assume an implication is that these devices then may not be passed
through to guests, yet I don't see us enforcing this anywhere.

--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -1494,8 +1494,8 @@ The following options are specific to In
     version 6 and greater as Registered-Based Invalidation isn't supported
     by them.
 
-*   The `igfx` boolean is active by default, and controls whether the IOMMU in
-    front of an Intel Graphics Device is enabled or not.
+*   The `igfx` boolean is active by default, and controls whether IOMMUs in
+    front of solely graphics devices get enabled or not.
 
     It is intended as a debugging mechanism for graphics issues, and to be
     similar to Linux's `intel_iommu=igfx_off` option.  If specifying `no-igfx`
--- a/xen/drivers/passthrough/vtd/dmar.c
+++ b/xen/drivers/passthrough/vtd/dmar.c
@@ -315,6 +315,7 @@ static int __init acpi_parse_dev_scope(
     struct acpi_drhd_unit *drhd = type == DMAR_TYPE ?
         container_of(scope, struct acpi_drhd_unit, scope) : NULL;
     int depth, cnt, didx = 0, ret;
+    bool gfx_only = false;
 
     if ( (cnt = scope_device_count(start, end)) < 0 )
         return cnt;
@@ -324,6 +325,8 @@ static int __init acpi_parse_dev_scope(
         scope->devices = xzalloc_array(u16, cnt);
         if ( !scope->devices )
             return -ENOMEM;
+
+        gfx_only = drhd && !drhd->include_all;
     }
     scope->devices_cnt = cnt;
 
@@ -354,6 +357,7 @@ static int __init acpi_parse_dev_scope(
                        acpi_scope->bus, sec_bus, sub_bus);
 
             dmar_scope_add_buses(scope, sec_bus, sub_bus);
+            gfx_only = false;
             break;
 
         case ACPI_DMAR_SCOPE_TYPE_HPET:
@@ -374,6 +378,8 @@ static int __init acpi_parse_dev_scope(
                 acpi_hpet_unit->dev = path->dev;
                 acpi_hpet_unit->func = path->fn;
                 list_add(&acpi_hpet_unit->list, &drhd->hpet_list);
+
+                gfx_only = false;
             }
 
             break;
@@ -388,6 +394,12 @@ static int __init acpi_parse_dev_scope(
                 if ( (seg == 0) && (bus == 0) && (path->dev == 2) &&
                      (path->fn == 0) )
                     igd_drhd_address = drhd->address;
+
+                if ( gfx_only &&
+                     pci_conf_read8(PCI_SBDF(seg, bus, path->dev, path->fn),
+                                    PCI_CLASS_DEVICE + 1) != 0x03
+                                    /* PCI_BASE_CLASS_DISPLAY */ )
+                    gfx_only = false;
             }
 
             break;
@@ -408,6 +420,8 @@ static int __init acpi_parse_dev_scope(
                 acpi_ioapic_unit->ioapic.bdf.dev = path->dev;
                 acpi_ioapic_unit->ioapic.bdf.func = path->fn;
                 list_add(&acpi_ioapic_unit->list, &drhd->ioapic_list);
+
+                gfx_only = false;
             }
 
             break;
@@ -417,11 +431,15 @@ static int __init acpi_parse_dev_scope(
                 printk(XENLOG_WARNING VTDPREFIX "Unknown scope type %#x\n",
                        acpi_scope->entry_type);
             start += acpi_scope->length;
+            gfx_only = false;
             continue;
         }
         scope->devices[didx++] = PCI_BDF(bus, path->dev, path->fn);
         start += acpi_scope->length;
-   }
+    }
+
+    if ( drhd && gfx_only )
+        drhd->gfx_only = true;
 
     ret = 0;
 
--- a/xen/drivers/passthrough/vtd/dmar.h
+++ b/xen/drivers/passthrough/vtd/dmar.h
@@ -62,7 +62,8 @@ struct acpi_drhd_unit {
     struct list_head list;
     u64    address;                     /* register base address of the unit */
     u16    segment;
-    u8     include_all:1;
+    bool   include_all:1;
+    bool   gfx_only:1;
     struct vtd_iommu *iommu;
     struct list_head ioapic_list;
     struct list_head hpet_list;
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -751,7 +751,7 @@ static void iommu_enable_translation(str
     unsigned long flags;
     struct vtd_iommu *iommu = drhd->iommu;
 
-    if ( is_igd_drhd(drhd) )
+    if ( drhd->gfx_only )
     {
         if ( !iommu_igfx )
         {