[PATCH v10 7/10] xen: implement new foreign copy hypercall

[Frediano Ziglio <freddy77@gmail.com>]

Add a sub hypercall to __HYPERVISOR_memory_op to allow to read/write
memory from/to a foreign domain.

Extending MMUEXT_COPY_PAGE seems better on first sight but considering
that MMUEXT is meant for PV only and trying to change that sub-op this
solution is better.

Signed-off-by: Frediano Ziglio <frediano.ziglio@citrix.com>
---
Changes since v4:
- Fix typo in comment.

Changes since v5:
- update xen_foreigncopy structure comments;
- move check for no frames after checking the domain;
- use mnemonic instead of 1U;
- fix page type checks;
- do not overwrite error copying back structure;
- latch MFN value;
- improved commit message.

Changes since v6:
- check permissions before nr_frames;
- different flag for read or write;
- print error as negative for coherence;
- update some comments;
- different page types for different architectures.

Changes since v9:
- page permission checks like MMU_UPDATE;
- new XSM settings;
- do not restrict domain;
- different explanation why HVM guests are not supported.
---
 xen/common/memory.c         | 149 ++++++++++++++++++++++++++++++++++++
 xen/include/public/memory.h |  45 ++++++++++-
 xen/include/xsm/dummy.h     |  14 ++++
 xen/include/xsm/hooks.h     |   2 +
 xen/xsm/flask/hooks.c       |  10 +++
 5 files changed, 219 insertions(+), 1 deletion(-)

diff --git a/xen/common/memory.c b/xen/common/memory.c
index 9443e35a7f..29a70d99b1 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -1548,6 +1548,141 @@ static int acquire_resource(
     return rc;
 }
 
+/*
+ * The "noinline" qualifier avoids the compiler to create a large function
+ * consuming quite a lot of stack.
+ */
+static int noinline mem_foreigncopy(
+    XEN_GUEST_HANDLE_PARAM(xen_foreigncopy_t) arg)
+{
+    struct domain *d, *const currd = current->domain;
+    xen_foreigncopy_t copy;
+    int rc, direction;
+
+    if ( copy_from_guest(&copy, arg, 1) )
+        return -EFAULT;
+
+    if ( copy.flags & ~XENMEM_foreigncopy_direction )
+        return -EINVAL;
+
+    direction = copy.flags & XENMEM_foreigncopy_direction;
+
+    d = rcu_lock_domain_by_any_id(copy.domid);
+    if ( !d )
+        return -ESRCH;
+
+    /*
+     * Check we are allowed to map and access these foreign pages.
+     */
+    if ( direction == XENMEM_foreigncopy_from )
+        rc = xsm_foreigncopy_from(XSM_TARGET, currd, d);
+    else
+        rc = xsm_foreigncopy_to(XSM_TARGET, currd, d);
+    if ( rc )
+        goto out;
+
+    while ( copy.nr_frames )
+    {
+        /*
+         * Arbitrary size.  Not too much stack space, and a reasonable stride
+         * for continuation checks.
+         */
+        xen_pfn_t gfn_list[32];
+        unsigned int todo = MIN(ARRAY_SIZE(gfn_list), copy.nr_frames);
+
+        rc = -EFAULT;
+        if ( copy_from_guest(gfn_list, copy.frame_list, todo) )
+            goto out;
+
+        for ( unsigned int i = 0; i < todo; i++ )
+        {
+            struct page_info *foreign_page;
+            mfn_t foreign_mfn;
+            void *foreign;
+            p2m_type_t p2mt;
+            p2m_query_t q = (direction == XENMEM_foreigncopy_to) ?
+                            P2M_ALLOC | P2M_UNSHARE : P2M_ALLOC;
+
+            foreign_page = get_page_from_gfn(d, gfn_list[i], &p2mt, q);
+
+            if ( unlikely(p2m_is_paged(p2mt)) )
+            {
+                if ( foreign_page )
+                    put_page(foreign_page);
+                p2m_mem_paging_populate(d, _gfn(gfn_list[i]));
+                p2mt = p2m_ram_paging_in;
+                foreign_page = NULL;
+            }
+
+            if ( unlikely(!foreign_page) )
+            {
+                rc = -ENOENT;
+                if ( p2mt != p2m_ram_paging_in )
+                {
+                    gdprintk(XENLOG_WARNING,
+                             "Error accessing foreign gfn %" PRI_gfn "\n",
+                             gfn_list[i]);
+                    rc = -EINVAL;
+                }
+                copy.nr_frames -= i;
+                guest_handle_add_offset(copy.frame_list, i);
+                goto out;
+            }
+
+            foreign_mfn = page_to_mfn(foreign_page);
+
+            /* A page is dirtied when it's being copied to. */
+            if ( direction == XENMEM_foreigncopy_to )
+                paging_mark_dirty(d, foreign_mfn);
+
+            foreign = map_domain_page(foreign_mfn);
+            if ( direction == XENMEM_foreigncopy_from )
+                rc = copy_to_guest(copy.buffer, foreign, PAGE_SIZE);
+            else
+                rc = copy_from_guest(foreign, copy.buffer, PAGE_SIZE);
+            unmap_domain_page(foreign);
+            put_page(foreign_page);
+
+            if ( unlikely(rc) )
+            {
+                gdprintk(XENLOG_WARNING,
+                         "Error %d copying gfn %" PRI_gfn "\n",
+                         rc, gfn_list[i]);
+                copy.nr_frames -= i;
+                guest_handle_add_offset(copy.frame_list, i);
+                goto out;
+            }
+
+            guest_handle_add_offset(copy.buffer, PAGE_SIZE);
+        }
+
+        copy.nr_frames -= todo;
+        guest_handle_add_offset(copy.frame_list, todo);
+
+        if ( copy.nr_frames && hypercall_preempt_check() )
+        {
+            rc = hypercall_create_continuation(
+                __HYPERVISOR_memory_op, "lh", XENMEM_foreigncopy, arg);
+            goto out;
+        }
+    }
+
+    rc = 0;
+
+ out:
+    rcu_unlock_domain(d);
+
+    /*
+     * Update in all cases, it allows the caller to know how many
+     * frames were successfully copied and the continuation to
+     * continue correctly.
+     */
+    if ( __copy_to_guest(arg, &copy, 1) && rc >= 0 )
+        rc = -EFAULT;
+
+    return rc;
+}
+
 long do_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
 {
     struct domain *d, *curr_d = current->domain;
@@ -2027,6 +2162,20 @@ long do_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
             start_extent);
         break;
 
+    case XENMEM_foreigncopy:
+        /*
+         * Instead of using "start_extent" for the continuation, we update
+         * the xen_foreigncopy structure back, so we are not constrained by
+         * MEMOP_EXTENT_SHIFT.
+         * We copy it back also to tell the caller where the copy stopped
+         * (either for error or because all frames were copied).
+         */
+        if ( unlikely(start_extent) )
+            return -EINVAL;
+
+        rc = mem_foreigncopy(guest_handle_cast(arg, xen_foreigncopy_t));
+        break;
+
     default:
         rc = arch_memory_op(cmd, arg);
         break;
diff --git a/xen/include/public/memory.h b/xen/include/public/memory.h
index bd9fc37b52..66bd2a6c42 100644
--- a/xen/include/public/memory.h
+++ b/xen/include/public/memory.h
@@ -740,7 +740,50 @@ struct xen_vnuma_topology_info {
 typedef struct xen_vnuma_topology_info xen_vnuma_topology_info_t;
 DEFINE_XEN_GUEST_HANDLE(xen_vnuma_topology_info_t);
 
-/* Next available subop number is 29 */
+/*
+ * Copy memory from/to a given domain.
+ * This calls is meant to replace expensive operations during migration which
+ * are only supported for PV guests.
+ */
+#define XENMEM_foreigncopy 29
+struct xen_foreigncopy {
+    /* IN - The domain whose memory is to be copied. */
+    domid_t domid;
+
+    /* IN - Flags. */
+#define XENMEM_foreigncopy_from 0
+#define XENMEM_foreigncopy_to 1
+#define XENMEM_foreigncopy_direction 1
+    uint16_t flags;
+
+    /*
+     * IN/OUT
+     *
+     * As an IN parameter number of frames of the domain to be copied.
+     * On output updated number of frames left (0 if success).
+     */
+    uint32_t nr_frames;
+
+    /*
+     * IN/OUT
+     *
+     * Frames to be copied.
+     * On output updated to point to the first frame unhandled, if any.
+     */
+    XEN_GUEST_HANDLE(xen_pfn_t) frame_list;
+
+    /*
+     * IN/OUT
+     *
+     * Guest buffer to read/write from.
+     * On output updated to point to the first page pointer unhandled.
+     */
+    XEN_GUEST_HANDLE(uint8) buffer;
+};
+typedef struct xen_foreigncopy xen_foreigncopy_t;
+DEFINE_XEN_GUEST_HANDLE(xen_foreigncopy_t);
+
+/* Next available subop number is 30 */
 
 #endif /* __XEN_PUBLIC_MEMORY_H__ */
 
diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index 131631cb27..dcdb7f5396 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -569,6 +569,20 @@ static XSM_INLINE int cf_check xsm_map_gmfn_foreign(
     return xsm_default_action(action, d, t);
 }
 
+static XSM_INLINE int cf_check xsm_foreigncopy_from(
+    XSM_DEFAULT_ARG struct domain *d, struct domain *t)
+{
+    XSM_ASSERT_ACTION(XSM_TARGET);
+    return xsm_default_action(action, d, t);
+}
+
+static XSM_INLINE int cf_check xsm_foreigncopy_to(
+    XSM_DEFAULT_ARG struct domain *d, struct domain *t)
+{
+    XSM_ASSERT_ACTION(XSM_TARGET);
+    return xsm_default_action(action, d, t);
+}
+
 #ifdef CONFIG_HVM
 
 static XSM_INLINE int cf_check xsm_hvm_param(
diff --git a/xen/include/xsm/hooks.h b/xen/include/xsm/hooks.h
index 5bdb23f26d..63e2831d31 100644
--- a/xen/include/xsm/hooks.h
+++ b/xen/include/xsm/hooks.h
@@ -58,6 +58,8 @@ XSM_HOOK(int, add_to_physmap, struct domain *, struct domain *)
 XSM_HOOK(int, remove_from_physmap, struct domain *, struct domain *)
 XSM_HOOK(int, map_gmfn_foreign, struct domain *, struct domain *)
 XSM_HOOK(int, claim_pages, struct domain *)
+XSM_HOOK(int, foreigncopy_from, struct domain *, struct domain *);
+XSM_HOOK(int, foreigncopy_to, struct domain *, struct domain *);
 
 XSM_HOOK(int, console_io, struct domain *, int)
 
diff --git a/xen/xsm/flask/hooks.c b/xen/xsm/flask/hooks.c
index 3cfdf6bf08..281800e176 100644
--- a/xen/xsm/flask/hooks.c
+++ b/xen/xsm/flask/hooks.c
@@ -1368,6 +1368,16 @@ static int cf_check flask_map_gmfn_foreign(struct domain *d, struct domain *t)
     return domain_has_perm(d, t, SECCLASS_MMU, MMU__MAP_READ | MMU__MAP_WRITE);
 }
 
+static int cf_check flask_foreigncopy_from(struct domain *d, struct domain *t)
+{
+    return domain_has_perm(d, t, SECCLASS_MMU, MMU__MAP_READ);
+}
+
+static int cf_check flask_foreigncopy_to(struct domain *d, struct domain *t)
+{
+    return domain_has_perm(d, t, SECCLASS_MMU, MMU__MAP_READ | MMU__MAP_WRITE);
+}
+
 #ifdef CONFIG_HVM
 
 static int cf_check flask_hvm_param(struct domain *d, unsigned long op)
-- 
2.43.0