[Xen-devel,09/12] xen/arm: mm: Use {, un}map_domain_page() to map/unmap Xen page-tables

Message ID 20190424165955.23718-10-julien.grall@arm.com
State Superseded
Headers show
Series
  • xen/arm: Provide a generic function to update Xen PT
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Commit Message

Julien Grall April 24, 2019, 4:59 p.m.
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 practice
all the page-tables updated will reside in xenheap, in practive 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@arm.com>
---
 xen/arch/arm/mm.c | 26 ++++++++++++++++++++++----
 1 file changed, 22 insertions(+), 4 deletions(-)

Comments

Andrii Anisov May 6, 2019, 12:48 p.m. | #1
On 24.04.19 19:59, Julien Grall wrote:
> 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 practice
> all the page-tables updated will reside in xenheap, in practive 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@arm.com>
> ---
> 


Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>

Patch

diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index 97e876d866..115e8340f1 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -969,6 +969,16 @@  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)
 {
@@ -1031,6 +1041,7 @@  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;
 
@@ -1049,15 +1060,17 @@  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) )
@@ -1082,7 +1095,12 @@  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);