x86/shadow: make iommu_snoop usage consistent with HAP's

First of all the variable is meaningful only when an IOMMU is in use for
a guest. Qualify the check accordingly, like done elsewhere. Furthermore
the controlling command line option is supposed to take effect on VT-d
only. Since command line parsing happens before we know whether we're
going to use VT-d, force the variable back to set when instead running
with AMD IOMMU(s).

Since it may end up misleading, also remove the clearing of the flag in
iommu_setup() and vtd_setup()'s error path. The variable simply is
meaningless with IOMMU(s) disabled, so there's no point touching it
there.

Finally also correct a relevant nearby comment.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Xenia Ragiadakou <burzalodowa@gmail.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>

diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
index cded39ef09942f4e1d3958d1535ed8ff701a2d83..5f3e175bbe034cd044623a4778c0e8d9199981bd 100644 (file)
--- a/xen/arch/x86/mm/shadow/multi.c
+++ b/xen/arch/x86/mm/shadow/multi.c
@@ -556,8 +556,8 @@ _sh_propagate(struct vcpu *v,
 
         ASSERT(!(sflags & PAGE_CACHE_ATTRS));
 
-        /* compute the PAT index for shadow page entry when VT-d is enabled
-         * and device assigned.
+        /*
+         * Compute the PAT index for shadow page entry when IOMMU is enabled.
          * 1) direct MMIO: compute the PAT index with gMTRR=UC and gPAT.
          * 2) if enables snoop control, compute the PAT index as WB.
          * 3) if disables snoop control, compute the PAT index with
@@ -577,7 +577,7 @@ _sh_propagate(struct vcpu *v,
                             gfn_to_paddr(target_gfn),
                             mfn_to_maddr(target_mfn),
                             X86_MT_UC);
-                else if ( iommu_snoop )
+                else if ( is_iommu_enabled(d) && iommu_snoop )
                     sflags |= pat_type_2_pte_flags(X86_MT_WB);
                 else
                     sflags |= get_pat_flags(v,

diff --git a/xen/drivers/passthrough/iommu.c b/xen/drivers/passthrough/iommu.c
index b4dfa95dfd8e49b2c953d09bbfe5190ef04f7109..921b71e81904a60f5281a3b426fab38076e006ed 100644 (file)
--- a/xen/drivers/passthrough/iommu.c
+++ b/xen/drivers/passthrough/iommu.c
@@ -587,9 +587,6 @@ int __init iommu_setup(void)
     printk("I/O virtualisation %sabled\n", iommu_enabled ? "en" : "dis");
     if ( !iommu_enabled )
     {
-#ifndef iommu_snoop
-        iommu_snoop = false;
-#endif
         iommu_hwdom_passthrough = false;
         iommu_hwdom_strict = false;
     }

diff --git a/xen/drivers/passthrough/vtd/iommu.c b/xen/drivers/passthrough/vtd/iommu.c
index 62e143125d99443e9949e51ccc65a1b92ff3b648..a9f4f28ad65c3a9e50d73468ac4867580b07066e 100644 (file)
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -2746,9 +2746,6 @@ static int __init cf_check vtd_setup(void)
 
  error:
     iommu_enabled = 0;
-#ifndef iommu_snoop
-    iommu_snoop = false;
-#endif
     iommu_hwdom_passthrough = false;
     iommu_qinval = 0;
     iommu_intremap = iommu_intremap_off;

diff --git a/xen/drivers/passthrough/x86/iommu.c b/xen/drivers/passthrough/x86/iommu.c
index f671b0f2bb45b22059a04be8f76d92c80b6700e9..5a8b28a4ca0e5bbef1418e68fd301ae986f6e96e 100644 (file)
--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -56,6 +56,17 @@ void __init acpi_iommu_init(void)
     if ( !acpi_disabled )
     {
         ret = acpi_dmar_init();
+
+#ifndef iommu_snoop
+        /*
+         * As long as there's no per-domain snoop control, and as long as on
+         * AMD we uniformly force coherent accesses, a possible command line
+         * override should affect VT-d only.
+         */
+        if ( ret )
+            iommu_snoop = true;
+#endif
+
         if ( ret == -ENODEV )
             ret = acpi_ivrs_init();
     }