[xen master] Revert "xen/arm32: head: Widen the use of the temporary mapping"

[patchbot@xxxxxxx]

commit c6c8c0808f908911a38bc330cdc7a26ac4bf6d51
Author:     Julien Grall <jgrall@xxxxxxxxxx>
AuthorDate: Fri Apr 21 11:01:06 2023 +0100
Commit:     Julien Grall <jgrall@xxxxxxxxxx>
CommitDate: Fri Apr 21 11:01:22 2023 +0100

    Revert "xen/arm32: head: Widen the use of the temporary mapping"
    
    We suspect the patch may break boot on the arndale board.
    
    This reverts commit eed3ae84bcd10a69c24c3cb4b0b98e070bc65ee4.
---
 xen/arch/arm/arm32/head.S | 86 ++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 70 insertions(+), 16 deletions(-)

diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index 5168eb4588..f9f7be9588 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -459,6 +459,7 @@ 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
         create_table_entry boot_second, boot_third, r0, 2
 
         /* Setup boot_third: */
@@ -478,37 +479,70 @@ create_page_tables:
         cmp   r1, #(XEN_PT_LPAE_ENTRIES<<3) /* 512*8-byte entries per page */
         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 the same
-         * as TEMPORARY_AREA_FIRST_SLOT, then we will want to switch
-         * to the temporary mapping before jumping to the runtime
-         * virtual mapping.
+         * 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.
          */
         get_table_slot r1, r9, 1     /* r1 := first slot */
-        cmp   r1, #TEMPORARY_AREA_FIRST_SLOT
-        bne   use_temporary_mapping
+        cmp   r1, #XEN_FIRST_SLOT
+        beq   1f
+        create_table_entry boot_pgtable, boot_second_id, r9, 1
+        b     link_from_second_id
 
-        mov_w r0, XEN_VIRT_START
-        create_table_entry boot_pgtable, boot_second, r0, 1
+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   r12, #0                /* r12 := temporary mapping not created */
         mov   pc, lr
 
-use_temporary_mapping:
+virtphys_clash:
         /*
-         * 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.
+         * 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.
          */
+        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
@@ -641,13 +675,33 @@ remove_identity_mapping:
         /* r2:r3 := invalid page-table entry */
         mov   r2, #0x0
         mov   r3, #0x0
-
-        /* Find the first slot used and remove it */
+        /*
+         * Find the first slot used. Remove the entry for the first
+         * table if the slot is not XEN_FIRST_SLOT.
+         */
         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)
--
generated by git-patchbot for /home/xen/git/xen.git#master