[xen master] xen/ppc: Relocate kernel to physical address 0 on boot

[patchbot@xxxxxxx]

commit 18b4f7e1e1a0ba0ad6df8643cfea560fc32b3ca9
Author:     Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>
AuthorDate: Wed Aug 23 09:28:02 2023 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Aug 23 09:28:02 2023 +0200

    xen/ppc: Relocate kernel to physical address 0 on boot
    
    Introduce a small assembly loop in `start` to copy the kernel to
    physical address 0 before continuing. This ensures that the physical
    address lines up with XEN_VIRT_START (0xc000000000000000) and allows us
    to identity map the kernel when the MMU is set up in the next patch.
    
    We are also able to start execution at XEN_VIRT_START after the copy
    since hardware will ignore the top 4 address bits when operating in Real
    Mode (MMU off).
    
    Signed-off-by: Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/ppc/include/asm/config.h |  2 +-
 xen/arch/ppc/ppc64/head.S         | 27 +++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/xen/arch/ppc/include/asm/config.h 
b/xen/arch/ppc/include/asm/config.h
index d060f0dca7..30438d22d2 100644
--- a/xen/arch/ppc/include/asm/config.h
+++ b/xen/arch/ppc/include/asm/config.h
@@ -39,7 +39,7 @@
     name:
 #endif
 
-#define XEN_VIRT_START _AT(UL, 0xc000000000000000)
+#define XEN_VIRT_START _AC(0xc000000000000000, UL)
 
 #define SMP_CACHE_BYTES (1 << 6)
 
diff --git a/xen/arch/ppc/ppc64/head.S b/xen/arch/ppc/ppc64/head.S
index 8f1e5d3ad2..a149339ad0 100644
--- a/xen/arch/ppc/ppc64/head.S
+++ b/xen/arch/ppc/ppc64/head.S
@@ -17,6 +17,33 @@ ENTRY(start)
     addis   %r2, %r12, .TOC.-1b@ha
     addi    %r2, %r2, .TOC.-1b@l
 
+    /*
+     * Copy Xen to physical address zero and jump to XEN_VIRT_START
+     * (0xc000000000000000). This works because the hardware will ignore the 
top
+     * four address bits when the MMU is off.
+     */
+    LOAD_REG_ADDR(%r14, _start)
+    LOAD_IMM64(%r12, XEN_VIRT_START)
+
+    /* If we're at the correct address, skip copy */
+    cmpld   %r14, %r12
+    beq     .L_correct_address
+
+    /* Copy bytes until _end */
+    LOAD_REG_ADDR(%r11, _end)
+    addi    %r14, %r14, -8
+    li      %r13, -8
+.L_copy_xen:
+    ldu     %r10, 8(%r14)
+    stdu    %r10, 8(%r13)
+    cmpld   %r14, %r11
+    blt     .L_copy_xen
+
+    /* Jump to XEN_VIRT_START */
+    mtctr   %r12
+    bctr
+.L_correct_address:
+
     /* set up the initial stack */
     LOAD_REG_ADDR(%r1, cpu0_boot_stack)
     li      %r11, 0
--
generated by git-patchbot for /home/xen/git/xen.git#master