[xen master] x86/shadow: make iommu_snoop usage consistent with HAP's

[patchbot@xxxxxxx]

commit c609108b2190d1ef43582c2b17b1b2e0beae0fb0
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Mon Feb 13 16:26:03 2023 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Feb 13 16:26:03 2023 +0100

    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@xxxxxxxx>
    Reviewed-by: Xenia Ragiadakou <burzalodowa@xxxxxxxxx>
    Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
---
 xen/arch/x86/mm/shadow/multi.c      |  6 +++---
 xen/drivers/passthrough/iommu.c     |  3 ---
 xen/drivers/passthrough/vtd/iommu.c |  3 ---
 xen/drivers/passthrough/x86/iommu.c | 11 +++++++++++
 4 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/xen/arch/x86/mm/shadow/multi.c b/xen/arch/x86/mm/shadow/multi.c
index cded39ef09..5f3e175bbe 100644
--- 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 b4dfa95dfd..921b71e819 100644
--- 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 62e143125d..a9f4f28ad6 100644
--- 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 f671b0f2bb..5a8b28a4ca 100644
--- 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();
     }
--
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