x86/ept: limit calls to memory_type_changed()

memory_type_changed() is currently only implemented for Intel EPT, and
results in the invalidation of EMT attributes on all the entries in
the EPT page tables.  Such invalidation causes EPT_MISCONFIG vmexits
when the guest tries to access any gfns for the first time, which
results in the recalculation of the EMT for the accessed page.  The
vmexit and the recalculations are expensive, and as such should be
avoided when possible.

Remove the call to memory_type_changed() from
XEN_DOMCTL_memory_mapping: there are no modifications of the
iomem_caps ranges anymore that could alter the return of
cache_flush_permitted() from that domctl.

Encapsulate calls to memory_type_changed() resulting from changes to
the domain iomem_caps or ioport_caps ranges in the helpers themselves
(io{ports,mem}_{permit,deny}_access()), and add a note in
epte_get_entry_emt() to remind that changes to the logic there likely
need to be propagaed to the IO capabilities helpers.

Note changes to the IO ports or memory ranges are not very common
during guest runtime, but Citrix Hypervisor has an use case for them
related to device passthrough.

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

xen/arch/x86/domctl.c

@@ -232,8 +232,6 @@ long arch_do_domctl(
             ret = ioports_permit_access(d, fp, fp + np - 1);
         else
             ret = ioports_deny_access(d, fp, fp + np - 1);
-        if ( !ret )
-            memory_type_changed(d);
         break;
     }
 
@@ -666,8 +664,6 @@ long arch_do_domctl(
                        "ioport_map: error %ld denying dom%d access to [%x,%x]\n",
                        ret, d->domain_id, fmp, fmp + np - 1);
         }
-        if ( !ret )
-            memory_type_changed(d);
         break;
     }
 

xen/arch/x86/include/asm/iocap.h

@@ -7,10 +7,11 @@
 #ifndef __X86_IOCAP_H__
 #define __X86_IOCAP_H__
 
-#define ioports_permit_access(d, s, e)                  \
-    rangeset_add_range((d)->arch.ioport_caps, s, e)
-#define ioports_deny_access(d, s, e)                    \
-    rangeset_remove_range((d)->arch.ioport_caps, s, e)
+#include <xen/sched.h>
+#include <xen/rangeset.h>
+
+#include <asm/p2m.h>
+
 #define ioports_access_permitted(d, s, e)               \
     rangeset_contains_range((d)->arch.ioport_caps, s, e)
 
@@ -18,4 +19,29 @@
     (!rangeset_is_empty((d)->iomem_caps) ||             \
      !rangeset_is_empty((d)->arch.ioport_caps))
 
+static inline int ioports_permit_access(struct domain *d, unsigned long s,
+                                        unsigned long e)
+{
+    bool flush = cache_flush_permitted(d);
+    int ret = rangeset_add_range(d->arch.ioport_caps, s, e);
+
+    if ( !ret && !is_iommu_enabled(d) && !flush )
+        /* See comment in iomem_permit_access(). */
+        memory_type_changed(d);
+
+    return ret;
+}
+
+static inline int ioports_deny_access(struct domain *d, unsigned long s,
+                                      unsigned long e)
+{
+    int ret = rangeset_remove_range(d->arch.ioport_caps, s, e);
+
+    if ( !ret && !is_iommu_enabled(d) && !cache_flush_permitted(d) )
+        /* See comment in iomem_deny_access(). */
+        memory_type_changed(d);
+
+    return ret;
+}
+
 #endif /* __X86_IOCAP_H__ */

xen/arch/x86/mm/p2m-ept.c

@@ -518,6 +518,10 @@ int epte_get_entry_emt(struct domain *d, gfn_t gfn, mfn_t mfn,
         return MTRR_TYPE_UNCACHABLE;
     }
 
+    /*
+     * Conditional must be kept in sync with the code in
+     * {iomem,ioports}_{permit,deny}_access().
+     */
     if ( type != p2m_mmio_direct && !is_iommu_enabled(d) &&
          !cache_flush_permitted(d) )
     {

xen/common/domctl.c

@@ -716,8 +716,6 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
             ret = iomem_permit_access(d, mfn, mfn + nr_mfns - 1);
         else
             ret = iomem_deny_access(d, mfn, mfn + nr_mfns - 1);
-        if ( !ret )
-            memory_type_changed(d);
         break;
     }
 
@@ -778,8 +776,6 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) u_domctl)
                        "memory_map: error %ld removing dom%d access to [%lx,%lx]\n",
                        ret, d->domain_id, mfn, mfn_end);
         }
-        /* Do this unconditionally to cover errors on above failure paths. */
-        memory_type_changed(d);
         break;
     }
 

xen/include/xen/iocap.h

@@ -7,13 +7,44 @@
 #ifndef __XEN_IOCAP_H__
 #define __XEN_IOCAP_H__
 
+#include <xen/sched.h>
 #include <xen/rangeset.h>
 #include <asm/iocap.h>
+#include <asm/p2m.h>
+
+static inline int iomem_permit_access(struct domain *d, unsigned long s,
+                                      unsigned long e)
+{
+    bool flush = cache_flush_permitted(d);
+    int ret = rangeset_add_range(d->iomem_caps, s, e);
+
+    if ( !ret && !is_iommu_enabled(d) && !flush )
+        /*
+         * Only flush if the range(s) are empty before this addition and
+         * IOMMU is not enabled for the domain, otherwise it makes no
+         * difference for effective cache attribute calculation purposes.
+         */
+        memory_type_changed(d);
+
+    return ret;
+}
+
+static inline int iomem_deny_access(struct domain *d, unsigned long s,
+                                    unsigned long e)
+{
+    int ret = rangeset_remove_range(d->iomem_caps, s, e);
+
+    if ( !ret && !is_iommu_enabled(d) && !cache_flush_permitted(d) )
+        /*
+         * Only flush if the range(s) are empty after this removal and
+         * IOMMU is not enabled for the domain, otherwise it makes no
+         * difference for effective cache attribute calculation purposes.
+         */
+        memory_type_changed(d);
+
+    return ret;
+}
 
-#define iomem_permit_access(d, s, e)                    \
-    rangeset_add_range((d)->iomem_caps, s, e)
-#define iomem_deny_access(d, s, e)                      \
-    rangeset_remove_range((d)->iomem_caps, s, e)
 #define iomem_access_permitted(d, s, e)                 \
     rangeset_contains_range((d)->iomem_caps, s, e)