[PATCH v2 1/3] x86/IOMMU: mark IOMMU / intremap not in use when ACPI tables are missing

[Jan Beulich <jbeulich@xxxxxxxx>]

x2apic_bsp_setup() gets called ahead of iommu_setup(), and since x2APIC
mode (physical vs clustered) depends on iommu_intremap, that variable
needs to be set to off as soon as we know we can't / won't enable
interrupt remapping, i.e. in particular when parsing of the respective
ACPI tables failed. Move the turning off of iommu_intremap from AMD
specific code into acpi_iommu_init(), accompanying it by clearing of
iommu_enable.

Take the opportunity and also fully skip ACPI table parsing logic on
VT-d when both "iommu=off" and "iommu=no-intremap" are in effect anyway,
like was already the case for AMD.

The tag below only references the commit uncovering a pre-existing
anomaly.

Fixes: d8bd82327b0f ("AMD/IOMMU: obtain IVHD type to use earlier")
Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
While the change here deals with apic_x2apic_probe() as called from
x2apic_bsp_setup(), the check_x2apic_preenabled() path looks to be
similarly affected. That call occurs before acpi_boot_init(), which is
what calls acpi_iommu_init(). The ordering in setup.c is in part
relatively fragile, which is why for the moment I'm still hesitant to
move the generic_apic_probe() call down. Plus I don't have easy access
to a suitable system to test this case. Thoughts?
---
v2: Treat iommu_enable and iommu_intremap as separate options.

--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c
@@ -183,9 +183,6 @@ int __init acpi_ivrs_init(void)
 {
     int rc;
 
-    if ( !iommu_enable && !iommu_intremap )
-        return 0;
-
     rc = amd_iommu_get_supported_ivhd_type();
     if ( rc < 0 )
         return rc;
@@ -193,10 +190,7 @@ int __init acpi_ivrs_init(void)
     ivhd_type = rc;
 
     if ( (amd_iommu_detect_acpi() !=0) || (iommu_found() == 0) )
-    {
-        iommu_intremap = iommu_intremap_off;
         return -ENODEV;
-    }
 
     iommu_init_ops = &_iommu_init_ops;
 
--- a/xen/drivers/passthrough/vtd/dmar.c
+++ b/xen/drivers/passthrough/vtd/dmar.c
@@ -777,11 +777,7 @@ static int __init acpi_parse_dmar(struct
     dmar = (struct acpi_table_dmar *)table;
     dmar_flags = dmar->flags;
 
-    if ( !iommu_enable && !iommu_intremap )
-    {
-        ret = -EINVAL;
-        goto out;
-    }
+    ASSERT(iommu_enable || iommu_intremap);
 
     if ( !dmar->width )
     {
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -41,6 +41,24 @@ enum iommu_intremap __read_mostly iommu_
 bool __read_mostly iommu_intpost;
 #endif
 
+void __init acpi_iommu_init(void)
+{
+    int ret;
+
+    if ( !iommu_enable && !iommu_intremap )
+        return;
+
+    ret = acpi_dmar_init();
+    if ( ret == -ENODEV )
+        ret = acpi_ivrs_init();
+
+    if ( ret )
+    {
+        iommu_enable = false;
+        iommu_intremap = iommu_intremap_off;
+    }
+}
+
 int __init iommu_hardware_setup(void)
 {
     struct IO_APIC_route_entry **ioapic_entries = NULL;
--- a/xen/include/asm-x86/acpi.h
+++ b/xen/include/asm-x86/acpi.h
@@ -141,16 +141,10 @@ extern u32 x86_acpiid_to_apicid[];
 extern u32 pmtmr_ioport;
 extern unsigned int pmtmr_width;
 
+void acpi_iommu_init(void);
 int acpi_dmar_init(void);
 int acpi_ivrs_init(void);
 
-static inline int acpi_iommu_init(void)
-{
-    int ret = acpi_dmar_init();
-
-    return ret == -ENODEV ? acpi_ivrs_init() : ret;
-}
-
 void acpi_mmcfg_init(void);
 
 /* Incremented whenever we transition through S3. Value is 1 during boot. */