xen: reinstate previously unused XENMEM_remove_from_physmap hypercall

This patch reinstates the XENMEM_remove_from_physmap hypercall
which was removed in 19041:ee62aaafff46 because it was not used.

However, is now needed in order to support xenstored stub domains.
The xenstored stub domain is not priviliged like dom0 and so cannot
unilaterally map the xenbus page of other guests into it's address
space.  Therefore, before creating a domU the domain builder needs to
seed its grant table with a grant ref allowing the xenstored stub
domain to access the new domU's xenbus page.

At present domU's do not start with their grant table mapped.
Instead it gets mapped when the guest requests a grant table from
the hypervisor.

In order to seed the grant table, the domain builder first needs to
map it into dom0 address space.  But the hypercall to do this
requires a gpfn (guest pfn), which is an mfn for PV guest, but a pfn
for HVM guests.  Therfore, in order to seed the grant table of an
HVM guest, dom0 needs to *temporarily* map it into the guest's
"physical" address space.

Hence the need to reinstate the XENMEM_remove_from_physmap hypercall.

Signed-off-by: Alex Zeffertt <alex.zeffertt@eu.citrix.com>
Signed-off-by: Daniel De Graaf <dgdegra@tycho.nsa.gov>
Acked-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Keir Fraser <keir@xen.org>

8 files changed, 87 insertions, 0 deletions

diff --git a/xen/common/compat/memory.c b/xen/common/compat/memory.c
index 2402984f1e..e7257cc53e 100644
--- a/xen/common/compat/memory.c
+++ b/xen/common/compat/memory.c
@@ -25,6 +25,7 @@ int compat_memory_op(unsigned int cmd, XEN_GUEST_HANDLE(void) compat)
             XEN_GUEST_HANDLE(void) hnd;
             struct xen_memory_reservation *rsrv;
             struct xen_memory_exchange *xchg;
+            struct xen_remove_from_physmap *xrfp;
         } nat;
         union {
             struct compat_memory_reservation rsrv;
@@ -179,6 +180,18 @@ int compat_memory_op(unsigned int cmd, XEN_GUEST_HANDLE(void) compat)
             nat.hnd = compat;
             break;
 
+        case XENMEM_remove_from_physmap:
+        {
+            struct compat_remove_from_physmap cmp;
+
+            if ( copy_from_guest(&cmp, compat, 1) )
+                return -EFAULT;
+
+            XLAT_remove_from_physmap(nat.xrfp, &cmp);
+
+            break;
+        }
+
         default:
             return compat_arch_memory_op(cmd, compat);
         }
@@ -284,6 +297,7 @@ int compat_memory_op(unsigned int cmd, XEN_GUEST_HANDLE(void) compat)
         case XENMEM_current_reservation:
         case XENMEM_maximum_reservation:
         case XENMEM_maximum_gpfn:
+        case XENMEM_remove_from_physmap:
             break;
 
         default:
diff --git a/xen/common/memory.c b/xen/common/memory.c
index 8d45439745..53886cea3b 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -659,6 +659,43 @@ long do_memory_op(unsigned long cmd, XEN_GUEST_HANDLE(void) arg)
 
         break;
 
+    case XENMEM_remove_from_physmap:
+    {
+        struct xen_remove_from_physmap xrfp;
+        unsigned long mfn;
+        struct domain *d;
+
+        if ( copy_from_guest(&xrfp, arg, 1) )
+            return -EFAULT;
+
+        rc = rcu_lock_target_domain_by_id(xrfp.domid, &d);
+        if ( rc != 0 )
+            return rc;
+
+        if ( xsm_remove_from_physmap(current->domain, d) )
+        {
+            rcu_unlock_domain(d);
+            return -EPERM;
+        }
+
+        domain_lock(d);
+
+        mfn = get_gfn_untyped(d, xrfp.gpfn);
+
+        if ( mfn_valid(mfn) )
+            guest_physmap_remove_page(d, xrfp.gpfn, mfn, PAGE_ORDER_4K);
+        else
+            rc = -ENOENT;
+
+        put_gfn(d, xrfp.gpfn);
+
+        domain_unlock(d);
+
+        rcu_unlock_domain(d);
+
+        break;
+    }
+
     default:
         rc = arch_memory_op(op, arg);
         break;
diff --git a/xen/include/asm-ia64/mm.h b/xen/include/asm-ia64/mm.h
index d09c363df3..a2bfc026e6 100644
--- a/xen/include/asm-ia64/mm.h
+++ b/xen/include/asm-ia64/mm.h
@@ -550,6 +550,7 @@ extern u64 translate_domain_pte(u64 pteval, u64 address, u64 itir__,
 #define gmfn_to_mfn(_d, gpfn)			\
     gmfn_to_mfn_foreign((_d), (gpfn))
 
+#define get_gfn_untyped(d, gpfn) gmfn_to_mfn(d, gpfn)
 #define put_gfn(d, g)   ((void)0)
 
 #define __gpfn_invalid(_d, gpfn)			\
diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
index 3bc2f25cdc..9d9aabcfdb 100644
--- a/xen/include/public/memory.h
+++ b/xen/include/public/memory.h
@@ -229,6 +229,22 @@ struct xen_add_to_physmap {
 typedef struct xen_add_to_physmap xen_add_to_physmap_t;
 DEFINE_XEN_GUEST_HANDLE(xen_add_to_physmap_t);
 
+/*
+ * Unmaps the page appearing at a particular GPFN from the specified guest's
+ * pseudophysical address space.
+ * arg == addr of xen_remove_from_physmap_t.
+ */
+#define XENMEM_remove_from_physmap      15
+struct xen_remove_from_physmap {
+    /* Which domain to change the mapping for. */
+    domid_t domid;
+
+    /* GPFN of the current mapping of the page. */
+    xen_pfn_t     gpfn;
+};
+typedef struct xen_remove_from_physmap xen_remove_from_physmap_t;
+DEFINE_XEN_GUEST_HANDLE(xen_remove_from_physmap_t);
+
 /*** REMOVED ***/
 /*#define XENMEM_translate_gpfn_list  8*/
 
diff --git a/xen/include/xlat.lst b/xen/include/xlat.lst
index f6021550df..3d4f1e328f 100644
--- a/xen/include/xlat.lst
+++ b/xen/include/xlat.lst
@@ -60,6 +60,7 @@
 !	memory_map			memory.h
 !	memory_reservation		memory.h
 !	pod_target			memory.h
+!	remove_from_physmap		memory.h
 ?	physdev_eoi			physdev.h
 ?	physdev_get_free_pirq		physdev.h
 ?	physdev_irq			physdev.h
diff --git a/xen/include/xsm/xsm.h b/xen/include/xsm/xsm.h
index df6cec22f3..566c8080f7 100644
--- a/xen/include/xsm/xsm.h
+++ b/xen/include/xsm/xsm.h
@@ -169,6 +169,7 @@ struct xsm_operations {
     int (*update_va_mapping) (struct domain *d, struct domain *f, 
                                                             l1_pgentry_t pte);
     int (*add_to_physmap) (struct domain *d1, struct domain *d2);
+    int (*remove_from_physmap) (struct domain *d1, struct domain *d2);
     int (*sendtrigger) (struct domain *d);
     int (*bind_pt_irq) (struct domain *d, struct xen_domctl_bind_pt_irq *bind);
     int (*unbind_pt_irq) (struct domain *d);
@@ -738,6 +739,11 @@ static inline int xsm_add_to_physmap(struct domain *d1, struct domain *d2)
     return xsm_call(add_to_physmap(d1, d2));
 }
 
+static inline int xsm_remove_from_physmap(struct domain *d1, struct domain *d2)
+{
+    return xsm_call(remove_from_physmap(d1, d2));
+}
+
 static inline int xsm_sendtrigger(struct domain *d)
 {
     return xsm_call(sendtrigger(d));
diff --git a/xen/xsm/dummy.c b/xen/xsm/dummy.c
index 4bbfbffb14..65daa4e775 100644
--- a/xen/xsm/dummy.c
+++ b/xen/xsm/dummy.c
@@ -529,6 +529,11 @@ static int dummy_add_to_physmap (struct domain *d1, struct domain *d2)
     return 0;
 }
 
+static int dummy_remove_from_physmap (struct domain *d1, struct domain *d2)
+{
+    return 0;
+}
+
 static int dummy_sendtrigger (struct domain *d)
 {
     return 0;
@@ -690,6 +695,7 @@ void xsm_fixup_ops (struct xsm_operations *ops)
     set_to_dummy_if_null(ops, mmu_machphys_update);
     set_to_dummy_if_null(ops, update_va_mapping);
     set_to_dummy_if_null(ops, add_to_physmap);
+    set_to_dummy_if_null(ops, remove_from_physmap);
     set_to_dummy_if_null(ops, sendtrigger);
     set_to_dummy_if_null(ops, bind_pt_irq);
     set_to_dummy_if_null(ops, pin_mem_cacheattr);
diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
index 0d35767821..a2020a9f60 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -1283,6 +1283,11 @@ static int flask_add_to_physmap(struct domain *d1, struct domain *d2)
     return domain_has_perm(d1, d2, SECCLASS_MMU, MMU__PHYSMAP);
 }
 
+static int flask_remove_from_physmap(struct domain *d1, struct domain *d2)
+{
+    return domain_has_perm(d1, d2, SECCLASS_MMU, MMU__PHYSMAP);
+}
+
 static int flask_sendtrigger(struct domain *d)
 {
     return domain_has_perm(current->domain, d, SECCLASS_DOMAIN, DOMAIN__TRIGGER);
@@ -1550,6 +1555,7 @@ static struct xsm_operations flask_ops = {
     .mmu_machphys_update = flask_mmu_machphys_update,
     .update_va_mapping = flask_update_va_mapping,
     .add_to_physmap = flask_add_to_physmap,
+    .remove_from_physmap = flask_remove_from_physmap,
     .sendtrigger = flask_sendtrigger,
     .get_device_group = flask_get_device_group,
     .test_assign_device = flask_test_assign_device,