[Xen-devel] [PATCH v2 05/20] arm64/alternatives: Make it possible to patch outside of hypervisor.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

With livepatching the alternatives that should be patched are
outside the Xen hypervisor _start -> _end. As such having
to use an alternative VA is not neccessary. In fact we
can use the ones that the caller provided us with.

Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Cc: Julien Grall <julien.grall@xxxxxxx>

v2: First version
---
 xen/arch/arm/alternative.c | 40 +++++++++++++++++++++++++---------------
 1 file changed, 25 insertions(+), 15 deletions(-)

diff --git a/xen/arch/arm/alternative.c b/xen/arch/arm/alternative.c
index aba06db..90a857a 100644
--- a/xen/arch/arm/alternative.c
+++ b/xen/arch/arm/alternative.c
@@ -94,24 +94,30 @@ static int __apply_alternatives(const struct alt_region 
*region)
 {
     const struct alt_instr *alt;
     const u32 *origptr, *replptr;
-    u32 *writeptr, *writemap;
+    u32 *writeptr, *writemap = NULL;
     mfn_t text_mfn = _mfn(virt_to_mfn(_stext));
     unsigned int text_order = get_order_from_bytes(_end - _start);
 
-    printk(XENLOG_INFO "alternatives: Patching kernel code\n");
-
-    /*
-     * The text section is read-only. So re-map Xen to be able to patch
-     * the code.
-     */
-    writemap = __vmap(&text_mfn, 1 << text_order, 1, 1, PAGE_HYPERVISOR,
-                      VMAP_DEFAULT);
-    if ( !writemap )
+    if ( region->begin >= __alt_instructions &&
+         region->end <= __alt_instructions_end )
     {
-        printk(XENLOG_ERR "alternatives: Unable to map the text section (size 
%u)\n",
-               1 << text_order);
-        return -ENOMEM;
+        printk(XENLOG_INFO "alternatives: Patching kernel code\n");
+        /*
+        * The text section is read-only. So re-map Xen to be able to patch
+        * the code.
+        */
+        writemap = __vmap(&text_mfn, 1 << text_order, 1, 1, PAGE_HYPERVISOR,
+                          VMAP_DEFAULT);
+        if ( !writemap )
+        {
+            printk(XENLOG_ERR "alternatives: Unable to map the text section 
(size %u)\n",
+                   1 << text_order);
+            return -ENOMEM;
+        }
     }
+    else
+        printk(XENLOG_INFO "alternatives: Patching %p -> %p\n",
+               region->begin, region->end);
 
     for ( alt = region->begin; alt < region->end; alt++ )
     {
@@ -124,8 +130,11 @@ static int __apply_alternatives(const struct alt_region 
*region)
         BUG_ON(alt->alt_len != alt->orig_len);
 
         origptr = ALT_ORIG_PTR(alt);
-        writeptr = origptr - (u32 *)_start + writemap;
         replptr = ALT_REPL_PTR(alt);
+        if ( writemap )
+            writeptr = origptr - (u32 *)_start + writemap;
+        else
+            writeptr = (u32 *)origptr;
 
         nr_inst = alt->alt_len / sizeof(insn);
 
@@ -143,7 +152,8 @@ static int __apply_alternatives(const struct alt_region 
*region)
     /* Nuke the instruction cache */
     invalidate_icache();
 
-    vunmap(writemap);
+    if ( writemap )
+        vunmap(writemap);
 
     return 0;
 }
-- 
2.4.11


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