[xen master] xen/riscv: introduce function for physical offset calculation

[patchbot@xxxxxxx]

commit af670c14e87a838d8274f5b619ce57379a749d93
Author:     Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
AuthorDate: Thu Nov 2 10:47:58 2023 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Nov 2 10:47:58 2023 +0100

    xen/riscv: introduce function for physical offset calculation
    
    The function was introduced to calculate and save physical
    offset before MMU is enabled because access to start() is
    PC-relative and in case of linker_addr != load_addr it will
    result in incorrect value in phys_offset.
    
    Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/riscv/include/asm/mm.h |  2 ++
 xen/arch/riscv/mm.c             | 21 ++++++++++++++++++---
 xen/arch/riscv/riscv64/head.S   | 14 ++++++++++++++
 3 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/xen/arch/riscv/include/asm/mm.h b/xen/arch/riscv/include/asm/mm.h
index 5e3ac5cde3..7b94cbadd7 100644
--- a/xen/arch/riscv/include/asm/mm.h
+++ b/xen/arch/riscv/include/asm/mm.h
@@ -15,4 +15,6 @@ void setup_initial_pagetables(void);
 void enable_mmu(void);
 void cont_after_mmu_is_enabled(void);
 
+unsigned long calc_phys_offset(void);
+
 #endif /* _ASM_RISCV_MM_H */
diff --git a/xen/arch/riscv/mm.c b/xen/arch/riscv/mm.c
index 99ed5e9623..a73f135a3c 100644
--- a/xen/arch/riscv/mm.c
+++ b/xen/arch/riscv/mm.c
@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#include <xen/cache.h>
 #include <xen/compiler.h>
 #include <xen/init.h>
 #include <xen/kernel.h>
@@ -19,9 +20,10 @@ struct mmu_desc {
     pte_t *pgtbl_base;
 };
 
-#define PHYS_OFFSET ((unsigned long)_start - XEN_VIRT_START)
-#define LOAD_TO_LINK(addr) ((addr) - PHYS_OFFSET)
-#define LINK_TO_LOAD(addr) ((addr) + PHYS_OFFSET)
+static unsigned long __ro_after_init phys_offset;
+
+#define LOAD_TO_LINK(addr) ((unsigned long)(addr) - phys_offset)
+#define LINK_TO_LOAD(addr) ((unsigned long)(addr) + phys_offset)
 
 /*
  * It is expected that Xen won't be more then 2 MB.
@@ -273,3 +275,16 @@ void __init noreturn noinline enable_mmu()
     switch_stack_and_jump((unsigned long)cpu0_boot_stack + STACK_SIZE,
                           cont_after_mmu_is_enabled);
 }
+
+/*
+ * calc_phys_offset() should be used before MMU is enabled because access to
+ * start() is PC-relative and in case when load_addr != linker_addr phys_offset
+ * will have an incorrect value
+ */
+unsigned long __init calc_phys_offset(void)
+{
+    volatile unsigned long load_start = (unsigned long)_start;
+
+    phys_offset = load_start - XEN_VIRT_START;
+    return phys_offset;
+}
diff --git a/xen/arch/riscv/riscv64/head.S b/xen/arch/riscv/riscv64/head.S
index 2c0304646a..ae194bb099 100644
--- a/xen/arch/riscv/riscv64/head.S
+++ b/xen/arch/riscv/riscv64/head.S
@@ -29,6 +29,20 @@ ENTRY(start)
 
         jal     reset_stack
 
+        /*
+         * save hart_id ( bootcpu_id ) and dtb_base as a0 and a1 register can
+         * be used by C code
+         */
+        mv      s0, a0
+        mv      s1, a1
+
+        jal     calc_phys_offset
+        mv      s2, a0
+
+        /* restore hart_id ( bootcpu_id ) and dtb address */
+        mv      a0, s0
+        mv      a1, s1
+
         tail    start_xen
 
         .section .text, "ax", %progbits
--
generated by git-patchbot for /home/xen/git/xen.git#master