[PATCH v2] IOMMU/x86: restrict IO-APIC mappings for PV Dom0

[Jan Beulich <jbeulich@xxxxxxxx>]

While already the case for PVH, there's no reason to treat PV
differently here (except of course where to take the addresses from).
Except that, to match CPU side mappings, by default we permit r/o ones
(which then also means to deal with IO-APICs whose MMIO is not covered
by E820 reserved regions).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Keep IOMMU mappings in sync with CPU ones.

--- a/xen/drivers/passthrough/x86/iommu.c
+++ b/xen/drivers/passthrough/x86/iommu.c
@@ -159,12 +159,12 @@ void arch_iommu_domain_destroy(struct do
            page_list_empty(&dom_iommu(d)->arch.pgtables.list));
 }
 
-static bool __hwdom_init hwdom_iommu_map(const struct domain *d,
-                                         unsigned long pfn,
-                                         unsigned long max_pfn)
+static unsigned int __hwdom_init hwdom_iommu_map(const struct domain *d,
+                                                 unsigned long pfn,
+                                                 unsigned long max_pfn)
 {
     mfn_t mfn = _mfn(pfn);
-    unsigned int i, type;
+    unsigned int i, type, perms = IOMMUF_readable | IOMMUF_writable;
 
     /*
      * Set up 1:1 mapping for dom0. Default to include only conventional RAM
@@ -173,44 +173,60 @@ static bool __hwdom_init hwdom_iommu_map
      * that fall in unusable ranges for PV Dom0.
      */
     if ( (pfn > max_pfn && !mfn_valid(mfn)) || xen_in_range(pfn) )
-        return false;
+        return 0;
 
     switch ( type = page_get_ram_type(mfn) )
     {
     case RAM_TYPE_UNUSABLE:
-        return false;
+        return 0;
 
     case RAM_TYPE_CONVENTIONAL:
         if ( iommu_hwdom_strict )
-            return false;
+            return 0;
         break;
 
     default:
         if ( type & RAM_TYPE_RESERVED )
         {
             if ( !iommu_hwdom_inclusive && !iommu_hwdom_reserved )
-                return false;
+                perms = 0;
         }
-        else if ( is_hvm_domain(d) || !iommu_hwdom_inclusive || pfn > max_pfn )
-            return false;
+        else if ( is_hvm_domain(d) )
+            return 0;
+        else if ( !iommu_hwdom_inclusive || pfn > max_pfn )
+            perms = 0;
     }
 
     /* Check that it doesn't overlap with the Interrupt Address Range. */
     if ( pfn >= 0xfee00 && pfn <= 0xfeeff )
-        return false;
+        return 0;
     /* ... or the IO-APIC */
-    for ( i = 0; has_vioapic(d) && i < d->arch.hvm.nr_vioapics; i++ )
-        if ( pfn == PFN_DOWN(domain_vioapic(d, i)->base_address) )
-            return false;
+    if ( has_vioapic(d) )
+    {
+        for ( i = 0; i < d->arch.hvm.nr_vioapics; i++ )
+            if ( pfn == PFN_DOWN(domain_vioapic(d, i)->base_address) )
+                return 0;
+    }
+    else if ( is_pv_domain(d) )
+    {
+        /*
+         * Be consistent with CPU mappings: Dom0 is permitted to establish r/o
+         * ones there, so it should also have such established for IOMMUs.
+         */
+        for ( i = 0; i < nr_ioapics; i++ )
+            if ( pfn == PFN_DOWN(mp_ioapics[i].mpc_apicaddr) )
+                return rangeset_contains_singleton(mmio_ro_ranges, pfn)
+                       ? IOMMUF_readable : 0;
+    }
     /*
      * ... or the PCIe MCFG regions.
      * TODO: runtime added MMCFG regions are not checked to make sure they
      * don't overlap with already mapped regions, thus preventing trapping.
      */
     if ( has_vpci(d) && vpci_is_mmcfg_address(d, pfn_to_paddr(pfn)) )
-        return false;
+        return 0;
 
-    return true;
+    return perms;
 }
 
 void __hwdom_init arch_iommu_hwdom_init(struct domain *d)
@@ -246,15 +262,19 @@ void __hwdom_init arch_iommu_hwdom_init(
     for ( i = 0; i < top; i++ )
     {
         unsigned long pfn = pdx_to_pfn(i);
+        unsigned int perms = hwdom_iommu_map(d, pfn, max_pfn);
         int rc;
 
-        if ( !hwdom_iommu_map(d, pfn, max_pfn) )
+        if ( !perms )
             rc = 0;
         else if ( paging_mode_translate(d) )
-            rc = set_identity_p2m_entry(d, pfn, p2m_access_rw, 0);
+            rc = set_identity_p2m_entry(d, pfn,
+                                        perms & IOMMUF_writable ? p2m_access_rw
+                                                                : p2m_access_r,
+                                        0);
         else
             rc = iommu_map(d, _dfn(pfn), _mfn(pfn), 1ul << PAGE_ORDER_4K,
-                           IOMMUF_readable | IOMMUF_writable, &flush_flags);
+                           perms, &flush_flags);
 
         if ( rc )
             printk(XENLOG_WARNING "%pd: identity %smapping of %lx failed: 
%d\n",