From 5e213f0f4d2ca4f286f8423316ed8090bcc5fef8 Mon Sep 17 00:00:00 2001
From: Julien Grall <jgrall@amazon.com>
Date: Mon, 24 Jul 2023 11:14:58 +0100
Subject: [PATCH] xen/arm32: head: Widen the use of the temporary mapping

At the moment, the temporary mapping is only used when the virtual
runtime region of Xen is clashing with the physical region.

In follow-up patches, we will rework how secondary CPU bring-up works
and it will be convenient to use the fixmap area for accessing
the root page-table (it is per-cpu).

Rework the code to use temporary mapping when the Xen physical address
is not overlapping with the temporary mapping.

This also has the advantage to simplify the logic to identity map
Xen.

Signed-off-by: Julien Grall <jgrall@amazon.com>

----

This patch was originally part of [1] but it was reverted due to
Xen not booting on the Arndale. The second patch of this series
is fixing it (confirmed by booting on the Arndale). So I am including
this patch.

[1] https://lore.kernel.org/xen-devel/20230416143211.72227-1-julien@xen.org/

Changes in new v2:
    - Rebase
    - Drop reviewed-by tags

Changelog from the previous series:

    Changes in v6:
        - Add Henry's reviewed-by and tested-by tag
        - Add Michal's reviewed-by
        - Add newline in remove_identity_mapping for clarity

    Changes in v5:
        - Fix typo in a comment
        - No need to link boot_{second, third}_id again if we need to
          create a temporary area.

    Changes in v3:
        - Resolve conflicts after switching from "ldr rX, <label>" to
          "mov_w rX, <label>" in a previous patch

Changes in v2:
        - Patch added

Reviewed-by: Henry Wang <Henry.Wang@arm.com>
Reviewed-by: Luca Fancellu <luca.fancellu@arm.com>
Tested-by: Luca Fancellu <luca.fancellu@arm.com>
---
 xen/arch/arm/arm32/head.S | 86 ++++++++-------------------------------
 1 file changed, 16 insertions(+), 70 deletions(-)

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index 26fc420b2e..33b038e7e0 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -473,7 +473,6 @@ ENDPROC(cpu_init)
 create_page_tables:
         /* Prepare the page-tables for mapping Xen */
         mov_w r0, XEN_VIRT_START
-        create_table_entry boot_pgtable, boot_second, r0, 1
 
         /*
          * We need to use a stash register because
@@ -519,70 +518,37 @@ create_page_tables:
         cmp   r1, r0                 /* Loop until we map all of Xen */
         blo   1b
 
-        /*
-         * If Xen is loaded at exactly XEN_VIRT_START then we don't
-         * need an additional 1:1 mapping, the virtual mapping will
-         * suffice.
-         */
-        cmp   r9, #XEN_VIRT_START
-        moveq pc, lr
-
         /*
          * Setup the 1:1 mapping so we can turn the MMU on. Note that
          * only the first page of Xen will be part of the 1:1 mapping.
-         *
-         * In all the cases, we will link boot_third_id. So create the
-         * mapping in advance.
          */
+        create_table_entry boot_pgtable, boot_second_id, r9, 1
+        create_table_entry boot_second_id, boot_third_id, r9, 2
         create_mapping_entry boot_third_id, r9, r9
 
         /*
-         * Find the first slot used. If the slot is not XEN_FIRST_SLOT,
-         * then the 1:1 mapping will use its own set of page-tables from
-         * the second level.
+         * Find the first slot used. If the slot is not the same
+         * as TEMPORARY_AREA_FIRST_SLOT, then we will want to switch
+         * to the temporary mapping before jumping to the runtime
+         * virtual mapping.
          */
         get_table_slot r1, r9, 1     /* r1 := first slot */
-        cmp   r1, #XEN_FIRST_SLOT
-        beq   1f
-        create_table_entry boot_pgtable, boot_second_id, r9, 1
-        b     link_from_second_id
+        cmp   r1, #TEMPORARY_AREA_FIRST_SLOT
+        bne   use_temporary_mapping
 
-1:
-        /*
-         * Find the second slot used. If the slot is XEN_SECOND_SLOT, then the
-         * 1:1 mapping will use its own set of page-tables from the
-         * third level.
-         */
-        get_table_slot r1, r9, 2     /* r1 := second slot */
-        cmp   r1, #XEN_SECOND_SLOT
-        beq   virtphys_clash
-        create_table_entry boot_second, boot_third_id, r9, 2
-        b     link_from_third_id
-
-link_from_second_id:
-        create_table_entry boot_second_id, boot_third_id, r9, 2
-link_from_third_id:
-        /* Good news, we are not clashing with Xen virtual mapping */
+        mov_w r0, XEN_VIRT_START
+        create_table_entry boot_pgtable, boot_second, r0, 1
         mov   r12, #0                /* r12 := temporary mapping not created */
         mov   pc, lr
 
-virtphys_clash:
+use_temporary_mapping:
         /*
-         * The identity map clashes with boot_third. Link boot_first_id and
-         * map Xen to a temporary mapping. See switch_to_runtime_mapping
-         * for more details.
+         * The identity mapping is not using the first slot
+         * TEMPORARY_AREA_FIRST_SLOT. Create a temporary mapping.
+         * See switch_to_runtime_mapping for more details.
          */
-        PRINT("- Virt and Phys addresses clash  -\r\n")
         PRINT("- Create temporary mapping -\r\n")
 
-        /*
-         * This will override the link to boot_second in XEN_FIRST_SLOT.
-         * The page-tables are not live yet. So no need to use
-         * break-before-make.
-         */
-        create_table_entry boot_pgtable, boot_second_id, r9, 1
-        create_table_entry boot_second_id, boot_third_id, r9, 2
-
         /* Map boot_second (cover Xen mappings) to the temporary 1st slot */
         mov_w r0, TEMPORARY_XEN_VIRT_START
         create_table_entry boot_pgtable, boot_second, r0, 1
@@ -720,33 +686,13 @@ remove_identity_mapping:
         /* r2:r3 := invalid page-table entry */
         mov   r2, #0x0
         mov   r3, #0x0
-        /*
-         * Find the first slot used. Remove the entry for the first
-         * table if the slot is not XEN_FIRST_SLOT.
-         */
+
+        /* Find the first slot used and remove it */
         get_table_slot r1, r9, 1     /* r1 := first slot */
-        cmp   r1, #XEN_FIRST_SLOT
-        beq   1f
-        /* It is not in slot 0, remove the entry */
         mov_w r0, boot_pgtable       /* r0 := root table */
         lsl   r1, r1, #3             /* r1 := Slot offset */
         strd  r2, r3, [r0, r1]
-        b     identity_mapping_removed
 
-1:
-        /*
-         * Find the second slot used. Remove the entry for the first
-         * table if the slot is not XEN_SECOND_SLOT.
-         */
-        get_table_slot r1, r9, 2     /* r1 := second slot */
-        cmp   r1, #XEN_SECOND_SLOT
-        beq   identity_mapping_removed
-        /* It is not in slot 1, remove the entry */
-        mov_w r0, boot_second        /* r0 := second table */
-        lsl   r1, r1, #3             /* r1 := Slot offset */
-        strd  r2, r3, [r0, r1]
-
-identity_mapping_removed:
         flush_xen_tlb_local r0
         mov   pc, lr
 ENDPROC(remove_identity_mapping)