At the moment, the fixmap table is only hooked when earlyprintk is used.
This is fine today because in C land, the fixmap is not used by anyone
until the the boot CPU is switching to the runtime page-tables.
In the future, the boot CPU will not switch between page-tables to
avoid TLB incoherency. Thus, the fixmap table will need to be always
hooked beofre any use. Let's start doing it now in setup_fixmap().
Lastly, document the behavior and the main registers usage within the
function.
Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
---
Changes in v2:
- Patch added
---
xen/arch/arm/arm32/head.S | 19 ++++++++++++++++---
1 file changed, 16 insertions(+), 3 deletions(-)
diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index 56e2d09ed4..e0f8c2e0cb 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -536,8 +536,21 @@ identity_mapping_removed:
mov pc, lr
ENDPROC(remove_identity_mapping)
+/*
+ * Map the UART in the fixmap (when earlyprintk is used) and hook the
+ * fixmap table in the page tables.
+ *
+ * The fixmap cannot be mapped in create_page_tables because it may
+ * clash with the 1:1 mapping.
+ *
+ * Inputs:
+ * r10: Physical offset
+ * r11: Early UART base physical address
+ *
+ * Clobbers r1 - r4
+ */
setup_fixmap:
-#if defined(CONFIG_EARLY_PRINTK) /* Fixmap is only used by early printk */
+#if defined(CONFIG_EARLY_PRINTK)
/* Add UART to the fixmap table */
ldr r1, =xen_fixmap /* r1 := vaddr (xen_fixmap) */
lsr r2, r11, #THIRD_SHIFT
@@ -546,7 +559,7 @@ setup_fixmap:
orr r2, r2, #PT_LOWER(DEV_L3) /* r2:r3 := 4K dev map including UART
*/
mov r3, #0x0
strd r2, r3, [r1, #(FIXMAP_CONSOLE*8)] /* Map it in the first
fixmap's slot */
-1:
+#endif
