passthrough/vtd: Drop the "workaround_bios_bug" logic entirely

It turns out that this code was previously dead.

c/s dcf4179 " x86/mmcfg/drhd: Move acpi_mmcfg_init() call before calling
acpi_parse_dmar()" resulted in PCI segment 0 now having been initialised
enough for acpi_parse_one_drhd() to not take the

  /* Skip checking if segment is not accessible yet. */

path unconditionally.  However, some systems have DMAR tables which list
devices which are disabled by user choice (in particular, Dell PowerEdge R740
with I/O AT DMA disabled), and turning off all IOMMU functionality in this
case is entirely unhelpful behaviour.

Leave the warning which identifies the problematic devices, but drop the
remaining logic.  This leaves the system in better overall state, and working
in the same way that it did in previous releases.

Reported-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: George Dunlap <george.dunlap@citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>
(cherry picked from commit 74dadb8)

Author: andyhhp

docs/misc/xen-command-line.pandoc

@@ -1173,8 +1173,7 @@ detection of systems known to misbehave upon accesses to that port.
 ### iommu
     = List of [ <bool>, verbose, debug, force, required,
                 sharept, intremap, intpost,
-                snoop, qinval, igfx, workaround_bios_bug,
-                amd-iommu-perdev-intremap,
+                snoop, qinval, igfx, amd-iommu-perdev-intremap,
                 dom0-{passthrough,strict} ]
 
     All sub-options are boolean in nature.
@@ -1259,10 +1258,6 @@ The following options are specific to Intel VT-d hardware:
     similar to Linux's `intel_iommu=igfx_off` option.  If specifying `no-igfx`
     fixes anything, please report the problem.
 
-*   The `workaround_bios_bug` boolean is disabled by default.  It can be used
-    to ignore errors when parsing the ACPI tables, and finding a listed PCI
-    device which doesn't appear to exist in the system.
-
 The following options are specific to AMD-Vi hardware:
 
 *   The `amd-iommu-perdev-intremap` boolean controls whether the interrupt

xen/drivers/passthrough/iommu.c

@@ -30,7 +30,6 @@ bool_t __initdata iommu_enable = 1;
 bool_t __read_mostly iommu_enabled;
 bool_t __read_mostly force_iommu;
 bool_t __read_mostly iommu_verbose;
-bool_t __read_mostly iommu_workaround_bios_bug;
 bool_t __read_mostly iommu_igfx = 1;
 bool_t __read_mostly iommu_snoop = 1;
 bool_t __read_mostly iommu_qinval = 1;
@@ -74,8 +73,6 @@ static int __init parse_iommu_param(const char *s)
         else if ( (val = parse_boolean("force", s, ss)) >= 0 ||
                   (val = parse_boolean("required", s, ss)) >= 0 )
             force_iommu = val;
-        else if ( (val = parse_boolean("workaround_bios_bug", s, ss)) >= 0 )
-            iommu_workaround_bios_bug = val;
         else if ( (val = parse_boolean("igfx", s, ss)) >= 0 )
             iommu_igfx = val;
         else if ( (val = parse_boolean("verbose", s, ss)) >= 0 )

xen/drivers/passthrough/vtd/dmar.c

@@ -514,7 +514,7 @@ acpi_parse_one_drhd(struct acpi_dmar_header *header)
     else
     {
         u8 b, d, f;
-        unsigned int i = 0, invalid_cnt = 0;
+        unsigned int i = 0;
         union {
             const void *raw;
             const struct acpi_dmar_device_scope *scope;
@@ -536,37 +536,12 @@ acpi_parse_one_drhd(struct acpi_dmar_header *header)
             f = PCI_FUNC(dmaru->scope.devices[i]);
 
             if ( !pci_device_detect(drhd->segment, b, d, f) )
-            {
                 printk(XENLOG_WARNING VTDPREFIX
                        " Non-existent device (%04x:%02x:%02x.%u) in this DRHD's scope!\n",
                        drhd->segment, b, d, f);
-                invalid_cnt++;
-            }
         }
 
-        if ( invalid_cnt )
-        {
-            if ( iommu_workaround_bios_bug &&
-                 invalid_cnt == dmaru->scope.devices_cnt )
-            {
-                printk(XENLOG_WARNING VTDPREFIX
-                       "  Workaround BIOS bug: ignoring DRHD (no devices in its scope are PCI discoverable)\n");
-
-                scope_devices_free(&dmaru->scope);
-                iommu_free(dmaru);
-                xfree(dmaru);
-            }
-            else
-            {
-                printk(XENLOG_WARNING VTDPREFIX
-                       "  DRHD is invalid (some devices in its scope are not PCI discoverable)\n");
-                printk(XENLOG_WARNING VTDPREFIX
-                       "  Try \"iommu=force\" or \"iommu=workaround_bios_bug\" if you really want VT-d\n");
-                ret = -EINVAL;
-            }
-        }
-        else
-            acpi_register_drhd_unit(dmaru);
+        acpi_register_drhd_unit(dmaru);
     }
 
 out:

xen/include/xen/iommu.h

@@ -53,8 +53,7 @@ static inline bool_t dfn_eq(dfn_t x, dfn_t y)
 }
 
 extern bool_t iommu_enable, iommu_enabled;
-extern bool_t force_iommu, iommu_verbose;
-extern bool_t iommu_workaround_bios_bug, iommu_igfx;
+extern bool_t force_iommu, iommu_verbose, iommu_igfx;
 extern bool_t iommu_snoop, iommu_qinval, iommu_intremap, iommu_intpost;
 extern bool_t iommu_hap_pt_share;
 extern bool_t iommu_debug;