IOMMU/x86: restrict IO-APIC mappings for PV Dom0

While already the case for PVH, there's no reason to treat PV
differently here, though of course the addresses get taken from another
source in this case. Except that, to match CPU side mappings, by default
we permit r/o ones. This then also means we now deal consistently with
IO-APICs whose MMIO is or is not covered by E820 reserved regions.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>

xen/drivers/passthrough/x86/iommu.c

@@ -13,6 +13,7 @@
  */
 
 #include <xen/sched.h>
+#include <xen/iocap.h>
 #include <xen/iommu.h>
 #include <xen/paging.h>
 #include <xen/guest_access.h>
@@ -275,12 +276,12 @@ void iommu_identity_map_teardown(struct domain *d)
     }
 }
 
-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
@@ -289,44 +290,60 @@ static bool __hwdom_init hwdom_iommu_map(const struct domain *d,
      * 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 (also for e.g. HPET in certain cases), so it should also
+         * have such established for IOMMUs.
+         */
+        if ( iomem_access_permitted(d, pfn, pfn) &&
+             rangeset_contains_singleton(mmio_ro_ranges, pfn) )
+            perms = IOMMUF_readable;
+    }
     /*
      * ... 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)
@@ -368,15 +385,19 @@ void __hwdom_init arch_iommu_hwdom_init(struct domain *d)
     for ( ; 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 = p2m_add_identity_entry(d, pfn, p2m_access_rw, 0);
+            rc = p2m_add_identity_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",