[PATCH] 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 the
IOMMU, i.e. in particular when
- parsing of the respective ACPI tables failed,
- "iommu=off" is in effect, but not "iommu=no-intremap".
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 skip ACPI table parsing altogether when
"iommu=off" is in effect anyway.

Reported-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
I've deliberately not added a Fixes: tag here, as I'm of the opinion
that d8bd82327b0f ("AMD/IOMMU: obtain IVHD type to use earlier") only
uncovered a pre-existing anomaly. This particularly applies to the
"iommu=off" aspect. (This now allows me to remove an item from my TODO
list: I was meaning to figure out why one of my systems wouldn't come
up properly with "iommu=off", and I had never thought of combining this
with "no-intremap".)

Arguably "iommu=off" should turn off subordinate features in common
IOMMU code, but doing so in parse_iommu_param() would be wrong (as
there might be multiple "iommu=" to parse). This could be placed in
iommu_supports_x2apic(), but see the next item.

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?

--- a/xen/drivers/passthrough/amd/pci_amd_iommu.c
+++ b/xen/drivers/passthrough/amd/pci_amd_iommu.c
@@ -193,10 +193,7 @@ 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/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -41,6 +41,23 @@ enum iommu_intremap __read_mostly iommu_
 bool __read_mostly iommu_intpost;
 #endif
 
+void __init acpi_iommu_init(void)
+{
+    if ( iommu_enable )
+    {
+        int ret = acpi_dmar_init();
+
+        if ( ret == -ENODEV )
+            ret = acpi_ivrs_init();
+
+        if ( ret )
+            iommu_enable = false;
+    }
+
+    if ( !iommu_enable )
+        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. */