[Xen-devel] [PATCH MM-PART3 v3 6/9] xen/arm: mm: Use {, un}map_domain_page() to map/unmap Xen page-tables

[Julien Grall <julien.grall@xxxxxxx>]

Currently, the virtual address of the 3rd level page-tables is obtained
using mfn_to_virt().

On Arm32, mfn_to_virt can only work on xenheap page. While in theory
all the page-tables updated will reside in xenheap, in practice the
page-tables covering Xen memory (e.g xen_mapping) is part of Xen binary.

Furthermore, a follow-up change will update xen_pt_update_entry() to
walk all the levels and therefore be more generic. Some of the
page-tables will also part of Xen memory and therefore will not be
reachable using mfn_to_virt().

The easiest way to reach those pages is to use {, un}map_domain_page().
While on arm32 this means an extra mapping in the normal cases, this is not
very important as xen page-tables are not updated often.

In order to allow future change in the way Xen page-tables are mapped,
two new helpers are introduced to map/unmap the page-tables.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
Reviewed-by: Andrii Anisov <andrii_anisov@xxxxxxxx>

---
    Changes in v3:
        - Fix typo in the commit message
        - Add Stefano's acked-by

    Changes in v2:
        - Add Andrii's reviewed-by
---
 xen/arch/arm/mm.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 3f6d0e29d5..c3dd2c08ba 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -947,6 +947,16 @@ static int create_xen_table(lpae_t *entry)
     return 0;
 }
 
+static lpae_t *xen_map_table(mfn_t mfn)
+{
+    return map_domain_page(mfn);
+}
+
+static void xen_unmap_table(const lpae_t *table)
+{
+    unmap_domain_page(table);
+}
+
 /* Sanity check of the entry */
 static bool xen_pt_check_entry(lpae_t entry, mfn_t mfn, unsigned int flags)
 {
@@ -1016,6 +1026,7 @@ static bool xen_pt_check_entry(lpae_t entry, mfn_t mfn, 
unsigned int flags)
 static int xen_pt_update_entry(unsigned long addr, mfn_t mfn,
                                unsigned int flags)
 {
+    int rc;
     lpae_t pte, *entry;
     lpae_t *third = NULL;
 
@@ -1034,15 +1045,17 @@ static int xen_pt_update_entry(unsigned long addr, 
mfn_t mfn,
 
     BUG_ON(!lpae_is_valid(*entry));
 
-    third = mfn_to_virt(lpae_get_mfn(*entry));
+    third = xen_map_table(lpae_get_mfn(*entry));
     entry = &third[third_table_offset(addr)];
 
+    rc = -EINVAL;
     if ( !xen_pt_check_entry(*entry, mfn, flags) )
-        return -EINVAL;
+        goto out;
 
     /* If we are only populating page-table, then we are done. */
+    rc = 0;
     if ( flags & _PAGE_POPULATE )
-        return 0;
+        goto out;
 
     /* We are removing the page */
     if ( !(flags & _PAGE_PRESENT) )
@@ -1067,7 +1080,12 @@ static int xen_pt_update_entry(unsigned long addr, mfn_t 
mfn,
 
     write_pte(entry, pte);
 
-    return 0;
+    rc = 0;
+
+out:
+    xen_unmap_table(third);
+
+    return rc;
 }
 
 static DEFINE_SPINLOCK(xen_pt_lock);
-- 
2.11.0


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