[PATCH] VT-d: don't panic/warn on iommu=no-igfx

[Rusty Bird <rustybird@openmailbox.org>]

When operating on an Intel graphics device, iommu_enable_translation()
panicked (force_iommu==1) or warned (force_iommu==0) about the BIOS if
is_igd_vt_enabled_quirk() returned 0. That's good if the actual BIOS
problem has been detected. But since commit 1463411, returning 0 could
also happen if the user simply passed "iommu=no-igfx", in which case
bailing out _without_ the panic/warning would be more appropriate.

The panic broke the combination "iommu=force,no-igfx", and also the case
where "iommu=no-igfx" is passed but force_iommu=1 is set automatically
by x2apic_bsp_setup().

Move the iommu_igfx check from is_igd_vt_enabled_quirk() into its only
caller iommu_enable_translation(), and tweak the logic.

Signed-off-by: Rusty Bird <rustybird@openmailbox.org>
---

Notes:
    Best viewed with "git show --ignore-space-change --function-context"

 xen/drivers/passthrough/vtd/iommu.c  | 18 ++++++++++++------
 xen/drivers/passthrough/vtd/quirks.c |  3 ---
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index 19328f6..2849ea1 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -747,14 +747,20 @@ static void iommu_enable_translation(struct acpi_drhd_unit *drhd)
     unsigned long flags;
     struct iommu *iommu = drhd->iommu;
 
-    if ( is_igd_drhd(drhd) && !is_igd_vt_enabled_quirk() ) 
+    if ( is_igd_drhd(drhd) )
     {
-        if ( force_iommu )
-            panic("BIOS did not enable IGD for VT properly, crash Xen for security purpose");
+        if ( !iommu_igfx )
+            return;
 
-        printk(XENLOG_WARNING VTDPREFIX
-               "BIOS did not enable IGD for VT properly.  Disabling IGD VT-d engine.\n");
-        return;
+        if ( !is_igd_vt_enabled_quirk() )
+        {
+            if ( force_iommu )
+                panic("BIOS did not enable IGD for VT properly, crash Xen for security purpose");
+
+            printk(XENLOG_WARNING VTDPREFIX
+                   "BIOS did not enable IGD for VT properly.  Disabling IGD VT-d engine.\n");
+            return;
+        }
     }
 
     /* apply platform specific errata workarounds */
diff --git a/xen/drivers/passthrough/vtd/quirks.c b/xen/drivers/passthrough/vtd/quirks.c
index 91f96ac..5bbbd96 100644
--- a/xen/drivers/passthrough/vtd/quirks.c
+++ b/xen/drivers/passthrough/vtd/quirks.c
@@ -70,9 +70,6 @@ int is_igd_vt_enabled_quirk(void)
 {
     u16 ggc;
 
-    if ( !iommu_igfx )
-        return 0;
-
     if ( !IS_ILK(ioh_id) )
         return 1;
 
-- 
2.9.4


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