[Xen-changelog] [xen staging] x86/apic: force phys mode if interrupt remapping is disabled

[patchbot@xxxxxxx]

commit c08cbf7fb891943508956d85a83b8c1799b7dc2c
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Fri Dec 20 16:27:48 2019 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Dec 20 16:27:48 2019 +0100

    x86/apic: force phys mode if interrupt remapping is disabled
    
    Cluster mode can only be used with interrupt remapping support, since
    the top 16bits of the APIC ID are filled with the cluster ID, and
    hence on systems where the physical ID is still smaller than 255 the
    cluster ID is not. Force x2APIC to use physical mode if there's no
    interrupt remapping support.
    
    Note that this requires a further patch in order to enable x2APIC
    without interrupt remapping support.
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 docs/misc/xen-command-line.pandoc |  3 ++-
 xen/arch/x86/genapic/x2apic.c     | 16 +++++++++++++++-
 2 files changed, 17 insertions(+), 2 deletions(-)

diff --git a/docs/misc/xen-command-line.pandoc 
b/docs/misc/xen-command-line.pandoc
index cb54a000fc..981a5e2381 100644
--- a/docs/misc/xen-command-line.pandoc
+++ b/docs/misc/xen-command-line.pandoc
@@ -2322,7 +2322,8 @@ Permit use of x2apic setup for SMP environments.
 ### x2apic_phys (x86)
 > `= <boolean>`
 
-> Default: `true` if **FADT** mandates physical mode, `false` otherwise.
+> Default: `true` if **FADT** mandates physical mode or if interrupt remapping
+>          is not available, `false` otherwise.
 
 In the case that x2apic is in use, this option switches between physical and
 clustered mode.  The default, given no hint from the **FADT**, is cluster
diff --git a/xen/arch/x86/genapic/x2apic.c b/xen/arch/x86/genapic/x2apic.c
index d5a17f10d5..1cb16bc10d 100644
--- a/xen/arch/x86/genapic/x2apic.c
+++ b/xen/arch/x86/genapic/x2apic.c
@@ -226,7 +226,21 @@ boolean_param("x2apic_phys", x2apic_phys);
 const struct genapic *__init apic_x2apic_probe(void)
 {
     if ( x2apic_phys < 0 )
-        x2apic_phys = !!(acpi_gbl_FADT.flags & ACPI_FADT_APIC_PHYSICAL);
+    {
+        /*
+         * Force physical mode if there's no interrupt remapping support: The
+         * ID in clustered mode requires a 32 bit destination field due to
+         * the usage of the high 16 bits to hold the cluster ID.
+         */
+        x2apic_phys = !iommu_intremap ||
+                      (acpi_gbl_FADT.flags & ACPI_FADT_APIC_PHYSICAL);
+    }
+    else if ( !x2apic_phys && !iommu_intremap )
+    {
+        printk("WARNING: x2APIC cluster mode is not supported without 
interrupt remapping\n"
+               "x2APIC: forcing phys mode\n");
+        x2apic_phys = true;
+    }
 
     if ( x2apic_phys )
         return &apic_x2apic_phys;
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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