[Xen-devel] [v4][PATCH 02/19] xen/x86/p2m: introduce set_identity_p2m_entry

[Tiejun Chen <tiejun.chen@xxxxxxxxx>]

We will create this sort of identity mapping as follows:

If the gfn space is unoccupied, we just set the mapping. If space
is already occupied by desired identity mapping, do nothing.
Otherwise, failure is returned.

And we also add a returning value to guest_physmap_remove_page()
then make that as a better helper to clear such a p2m entry.

CC: Tim Deegan <tim@xxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Signed-off-by: Tiejun Chen <tiejun.chen@xxxxxxxxx>
Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
---
v4:

* Change that orginal condition,

  if ( p2mt == p2m_invalid || p2mt == p2m_mmio_dm )
  
  to make sure we catch those invalid mfn mapping as we expected.

* To have

  if ( !paging_mode_translate(p2m->domain) )
    return 0;

  at the start, instead of indenting the whole body of the function
  in an inner scope. 

* extend guest_physmap_remove_page() to return a value as a proper
  unmapping helper

 xen/arch/x86/mm/p2m.c     | 40 ++++++++++++++++++++++++++++++++++++++--
 xen/include/asm-x86/p2m.h | 10 +++++++---
 2 files changed, 45 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/mm/p2m.c b/xen/arch/x86/mm/p2m.c
index 1fd1194..7e50db6 100644
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -584,14 +584,16 @@ p2m_remove_page(struct p2m_domain *p2m, unsigned long 
gfn, unsigned long mfn,
                          p2m->default_access);
 }
 
-void
+int
 guest_physmap_remove_page(struct domain *d, unsigned long gfn,
                           unsigned long mfn, unsigned int page_order)
 {
     struct p2m_domain *p2m = p2m_get_hostp2m(d);
+    int rc;
     gfn_lock(p2m, gfn, page_order);
-    p2m_remove_page(p2m, gfn, mfn, page_order);
+    rc = p2m_remove_page(p2m, gfn, mfn, page_order);
     gfn_unlock(p2m, gfn, page_order);
+    return rc;
 }
 
 int
@@ -898,6 +900,40 @@ int set_mmio_p2m_entry(struct domain *d, unsigned long 
gfn, mfn_t mfn,
     return set_typed_p2m_entry(d, gfn, mfn, p2m_mmio_direct, access);
 }
 
+int set_identity_p2m_entry(struct domain *d, unsigned long gfn,
+                           p2m_access_t p2ma)
+{
+    p2m_type_t p2mt;
+    p2m_access_t a;
+    mfn_t mfn;
+    struct p2m_domain *p2m = p2m_get_hostp2m(d);
+    int ret;
+
+    if ( !paging_mode_translate(p2m->domain) )
+        return 0;
+
+    gfn_lock(p2m, gfn, 0);
+
+    mfn = p2m->get_entry(p2m, gfn, &p2mt, &a, 0, NULL);
+
+    if ( p2mt == p2m_invalid || p2mt == p2m_mmio_dm )
+        ret = p2m_set_entry(p2m, gfn, _mfn(gfn), PAGE_ORDER_4K,
+                            p2m_mmio_direct, p2ma);
+    else if ( mfn_x(mfn) == gfn && p2mt == p2m_mmio_direct && a == p2ma )
+        ret = 0;
+    else
+    {
+        ret = -EBUSY;
+        printk(XENLOG_G_WARNING
+               "Cannot setup identity map d%d:%lx,"
+               " gfn already mapped to %lx.\n",
+               d->domain_id, gfn, mfn_x(mfn));
+    }
+
+    gfn_unlock(p2m, gfn, 0);
+    return ret;
+}
+
 /* Returns: 0 for success, -errno for failure */
 int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn)
 {
diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
index b49c09b..538a1cf 100644
--- a/xen/include/asm-x86/p2m.h
+++ b/xen/include/asm-x86/p2m.h
@@ -503,9 +503,9 @@ static inline int guest_physmap_add_page(struct domain *d,
 }
 
 /* Remove a page from a domain's p2m table */
-void guest_physmap_remove_page(struct domain *d,
-                               unsigned long gfn,
-                               unsigned long mfn, unsigned int page_order);
+int guest_physmap_remove_page(struct domain *d,
+                              unsigned long gfn,
+                              unsigned long mfn, unsigned int page_order);
 
 /* Set a p2m range as populate-on-demand */
 int guest_physmap_mark_populate_on_demand(struct domain *d, unsigned long gfn,
@@ -543,6 +543,10 @@ int set_mmio_p2m_entry(struct domain *d, unsigned long 
gfn, mfn_t mfn,
                        p2m_access_t access);
 int clear_mmio_p2m_entry(struct domain *d, unsigned long gfn, mfn_t mfn);
 
+/* Set identity addresses in the p2m table (for pass-through) */
+int set_identity_p2m_entry(struct domain *d, unsigned long gfn,
+                           p2m_access_t p2ma);
+
 /* Add foreign mapping to the guest's p2m table. */
 int p2m_add_foreign(struct domain *tdom, unsigned long fgfn,
                     unsigned long gpfn, domid_t foreign_domid);
-- 
1.9.1


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