Re: [Xen-devel] [V6 PATCH 6.1/7] pvh dom0: Add and remove foreign pages

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

New version of the patch with xenmem_rem_foreign_from_p2m() created:

In this patch, a new function, xenmem_add_foreign_to_p2m(), is added
to map pages from foreign guest into current dom0 for domU creation.
Such pages are typed p2m_map_foreign. Another function
xenmem_rem_foreign_from_p2m() is added to remove such pages. Note, in
the remove path, we must release the refcount that was taken during
the map phase.

Signed-off-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
---
 xen/arch/x86/mm.c         |  114 ++++++++++++++++++++++++++++++++++++++++++---
 xen/common/memory.c       |   12 ++++-
 xen/include/asm-arm/p2m.h |    9 +++-
 xen/include/asm-x86/p2m.h |    3 +
 4 files changed, 128 insertions(+), 10 deletions(-)

diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c
index e3da479..78f4650 100644
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -2810,7 +2810,7 @@ static struct domain *get_pg_owner(domid_t domid)
         goto out;
     }
 
-    if ( unlikely(paging_mode_translate(curr)) )
+    if ( !is_pvh_domain(curr) && unlikely(paging_mode_translate(curr)) )
     {
         MEM_LOG("Cannot mix foreign mappings with translated domains");
         goto out;
@@ -4520,9 +4520,101 @@ static int handle_iomem_range(unsigned long s, unsigned 
long e, void *p)
     return 0;
 }
 
+/*
+ * Add frames from foreign domain to target domain's physmap. Similar to
+ * XENMAPSPACE_gmfn but the frame is foreign being mapped into current,
+ * and is not removed from foreign domain.
+ * Usage: libxl on pvh dom0 creating a guest and doing privcmd_ioctl_mmap.
+ * Side Effect: the mfn for fgfn will be refcounted so it is not lost
+ *              while mapped here. The refcnt is released in do_memory_op()
+ *              via XENMEM_remove_from_physmap.
+ * Returns: 0 ==> success
+ */
+static int xenmem_add_foreign_to_p2m(struct domain *tdom, unsigned long fgfn,
+                                     unsigned long gpfn, struct domain *fdom)
+{
+    p2m_type_t p2mt, p2mt_prev;
+    int rc = 0;
+    unsigned long prev_mfn, mfn = 0;
+    struct page_info *page = NULL;
+
+    if ( tdom == fdom || !tdom || !fdom || !is_pvh_domain(tdom) )
+        return -EINVAL;
+
+    /* following will take a refcnt on the mfn */
+    page = get_page_from_gfn(fdom, fgfn, &p2mt, P2M_ALLOC);
+    if ( !page || !p2m_is_valid(p2mt) )
+    {
+        if ( page )
+            put_page(page);
+        return -EINVAL;
+    }
+    mfn = page_to_mfn(page);
+
+    /* Remove previously mapped page if it is present. */
+    prev_mfn = mfn_x(get_gfn(tdom, gpfn, &p2mt_prev));
+    if ( mfn_valid(prev_mfn) )
+    {
+        if ( is_xen_heap_mfn(prev_mfn) )
+            /* Xen heap frames are simply unhooked from this phys slot */
+            guest_physmap_remove_page(tdom, gpfn, prev_mfn, 0);
+        else
+            /* Normal domain memory is freed, to avoid leaking memory. */
+            guest_remove_page(tdom, gpfn);
+    }
+    /*
+     * Create the new mapping. Can't use guest_physmap_add_page() because it
+     * will update the m2p table which will result in  mfn -> gpfn of dom0
+     * and not fgfn of domU.
+     */
+    if ( set_foreign_p2m_entry(tdom, gpfn, _mfn(mfn)) == 0 )
+    {
+        gdprintk(XENLOG_WARNING, "set_foreign_p2m_entry failed. "
+                 "gpfn:%lx mfn:%lx fgfn:%lx td:%d fd:%d\n",
+                 gpfn, mfn, fgfn, tdom->domain_id, fdom->domain_id);
+        put_page(page);
+        rc = -EINVAL;
+    }
+
+    /*
+     * We must do this put_gfn after set_foreign_p2m_entry so another cpu
+     * doesn't populate the gpfn before us.
+     */
+    put_gfn(tdom, gpfn);
+
+    return rc;
+}
+
+/* Note, the refcnt released here is taken in xenmem_add_foreign_to_p2m */
+int xenmem_rem_foreign_from_p2m(struct domain *d, unsigned long gpfn)
+{
+    unsigned long mfn;
+    p2m_type_t p2mt;
+    struct domain *foreign_dom;
+
+    mfn = mfn_x(get_gfn_query(d, gpfn, &p2mt));
+    if ( !mfn_valid(mfn) )
+    {
+        gdprintk(XENLOG_WARNING, "Invalid mfn for gpfn:%lx domid:%d\n",
+                 gpfn, d->domain_id);
+        return -EINVAL;
+    }
+
+    foreign_dom = page_get_owner(mfn_to_page(mfn));
+    ASSERT(d != foreign_dom);
+    ASSERT(is_pvh_domain(d));
+
+    guest_physmap_remove_page(d, gpfn, mfn, 0);
+    put_page(mfn_to_page(mfn));
+    put_gfn(d, gpfn);
+
+    return 0;
+}
+
 static int xenmem_add_to_physmap_once(
     struct domain *d,
-    const struct xen_add_to_physmap *xatp)
+    const struct xen_add_to_physmap *xatp,
+    struct domain *fdom)
 {
     struct page_info *page = NULL;
     unsigned long gfn = 0; /* gcc ... */
@@ -4581,6 +4673,13 @@ static int xenmem_add_to_physmap_once(
             page = mfn_to_page(mfn);
             break;
         }
+
+        case XENMAPSPACE_gmfn_foreign:
+        {
+            rc = xenmem_add_foreign_to_p2m(d, xatp->idx, xatp->gpfn, fdom);
+            return rc;
+        }
+
         default:
             break;
     }
@@ -4646,7 +4745,7 @@ static int xenmem_add_to_physmap(struct domain *d,
         start_xatp = *xatp;
         while ( xatp->size > 0 )
         {
-            rc = xenmem_add_to_physmap_once(d, xatp);
+            rc = xenmem_add_to_physmap_once(d, xatp, NULL);
             if ( rc < 0 )
                 return rc;
 
@@ -4672,11 +4771,12 @@ static int xenmem_add_to_physmap(struct domain *d,
         return rc;
     }
 
-    return xenmem_add_to_physmap_once(d, xatp);
+    return xenmem_add_to_physmap_once(d, xatp, NULL);
 }
 
 static int xenmem_add_to_physmap_range(struct domain *d,
-                                       struct xen_add_to_physmap_range *xatpr)
+                                       struct xen_add_to_physmap_range *xatpr,
+                                       struct domain *fdom)
 {
     /* Process entries in reverse order to allow continuations */
     while ( xatpr->size > 0 )
@@ -4693,7 +4793,7 @@ static int xenmem_add_to_physmap_range(struct domain *d,
         xatp.space = xatpr->space;
         xatp.idx = idx;
         xatp.gpfn = gpfn;
-        rc = xenmem_add_to_physmap_once(d, &xatp);
+        rc = xenmem_add_to_physmap_once(d, &xatp, fdom);
 
         if ( copy_to_guest_offset(xatpr->errs, xatpr->size-1, &rc, 1) )
             return -EFAULT;
@@ -4780,7 +4880,7 @@ long arch_memory_op(int op, XEN_GUEST_HANDLE_PARAM(void) 
arg)
         }
         rc = xsm_add_to_physmap(XSM_TARGET, current->domain, d, fd);
         if ( rc == 0 )
-            rc = xenmem_add_to_physmap_range(d, &xatpr);
+            rc = xenmem_add_to_physmap_range(d, &xatpr, fd);
 
         rcu_unlock_domain(d);
         if ( fd )
diff --git a/xen/common/memory.c b/xen/common/memory.c
index eb7b72b..80c660e 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -678,6 +678,7 @@ long do_memory_op(unsigned long cmd, 
XEN_GUEST_HANDLE_PARAM(void) arg)
         struct xen_remove_from_physmap xrfp;
         struct page_info *page;
         struct domain *d;
+        p2m_type_t p2mt;
 
         if ( copy_from_guest(&xrfp, arg, 1) )
             return -EFAULT;
@@ -693,12 +694,21 @@ long do_memory_op(unsigned long cmd, 
XEN_GUEST_HANDLE_PARAM(void) arg)
             return rc;
         }
 
-        page = get_page_from_gfn(d, xrfp.gpfn, NULL, P2M_ALLOC);
+        /*
+         * If autotranslate guest, (eg pvh), the gfn could be mapped to a mfn
+         * from foreign domain by the user space tool during domain creation.
+         * We need to check for that, free it up from the p2m, and release
+         * refcnt on it. In such a case, page would be NULL and the following
+         * call would not have refcnt'd the page.
+         */
+        page = get_page_from_gfn(d, xrfp.gpfn, &p2mt, P2M_ALLOC);
         if ( page )
         {
             guest_physmap_remove_page(d, xrfp.gpfn, page_to_mfn(page), 0);
             put_page(page);
         }
+        else if ( p2m_is_foreign(p2mt) )
+            rc = xenmem_rem_foreign_from_p2m(d, xrfp.gpfn);
         else
             rc = -ENOENT;
 
diff --git a/xen/include/asm-arm/p2m.h b/xen/include/asm-arm/p2m.h
index c660820..0c554a5 100644
--- a/xen/include/asm-arm/p2m.h
+++ b/xen/include/asm-arm/p2m.h
@@ -83,8 +83,6 @@ static inline struct page_info *get_page_from_gfn(
     struct page_info *page;
     unsigned long mfn = gmfn_to_mfn(d, gfn);
 
-    ASSERT(t == NULL);
-
     if (!mfn_valid(mfn))
         return NULL;
     page = mfn_to_page(mfn);
@@ -110,6 +108,13 @@ static inline int get_page_and_type(struct page_info *page,
     return rc;
 }
 
+#define p2m_is_foreign(_t) (0 && (_t))
+static inline int xenmem_rem_foreign_from_p2m(struct domain *d, 
+                                              unsigned long gpfn)
+{
+    return -ENOSYS;
+}
+
 #endif /* _XEN_P2M_H */
 
 /*
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index 6fc71a1..aacdffe 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -515,6 +515,9 @@ int clear_mmio_p2m_entry(struct domain *d, unsigned long 
gfn);
 /* Set foreign mfn in the current guest's p2m table. */
 int set_foreign_p2m_entry(struct domain *domp, unsigned long gfn, mfn_t mfn);
 
+/* Remove foreign mapping from the guest's p2m table. */
+int xenmem_rem_foreign_from_p2m(struct domain *d, unsigned long gpfn);
+
 /* 
  * Populate-on-demand
  */
-- 
1.7.2.3


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