ARM: P2V: introduce phys_to_virt/virt_to_phys runtime patching
This idea came from Nicolas, Eric Miao produced an initial version,
which was then rewritten into this.
Patch the physical to virtual translations at runtime. As we modify
the code, this makes it incompatible with XIP kernels, but allows us
to achieve this with minimal loss of performance.
As many translations are of the form:
physical = virtual + (PHYS_OFFSET - PAGE_OFFSET)
virtual = physical - (PHYS_OFFSET - PAGE_OFFSET)
we generate an 'add' instruction for __virt_to_phys(), and a 'sub'
instruction for __phys_to_virt(). We calculate at run time (PHYS_OFFSET
- PAGE_OFFSET) by comparing the address prior to MMU initialization with
where it should be once the MMU has been initialized, and place this
constant into the above add/sub instructions.
Once we have (PHYS_OFFSET - PAGE_OFFSET), we can calculate the real
PHYS_OFFSET as PAGE_OFFSET is a build-time constant, and save this for
the C-mode PHYS_OFFSET variable definition to use.
At present, we are unable to support Realview with Sparsemem enabled
as this uses a complex mapping function, and MSM as this requires a
constant which will not fit in our math instruction.
Add a module version magic string for this feature to prevent
incompatible modules being loaded.
Tested-by: Tony Lindgren <tony@atomide.com>
Reviewed-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Tested-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c
index e5e1e53..9615423 100644
--- a/arch/arm/kernel/armksyms.c
+++ b/arch/arm/kernel/armksyms.c
@@ -170,3 +170,7 @@
#endif
EXPORT_SYMBOL(__gnu_mcount_nc);
#endif
+
+#ifdef CONFIG_ARM_PATCH_PHYS_VIRT
+EXPORT_SYMBOL(__pv_phys_offset);
+#endif
diff --git a/arch/arm/kernel/head.S b/arch/arm/kernel/head.S
index 03a588b..1db8ead 100644
--- a/arch/arm/kernel/head.S
+++ b/arch/arm/kernel/head.S
@@ -98,6 +98,9 @@
#ifdef CONFIG_SMP_ON_UP
bl __fixup_smp
#endif
+#ifdef CONFIG_ARM_PATCH_PHYS_VIRT
+ bl __fixup_pv_table
+#endif
bl __create_page_tables
/*
@@ -438,4 +441,69 @@
#endif
+#ifdef CONFIG_ARM_PATCH_PHYS_VIRT
+
+/* __fixup_pv_table - patch the stub instructions with the delta between
+ * PHYS_OFFSET and PAGE_OFFSET, which is assumed to be 16MiB aligned and
+ * can be expressed by an immediate shifter operand. The stub instruction
+ * has a form of '(add|sub) rd, rn, #imm'.
+ */
+ __HEAD
+__fixup_pv_table:
+ adr r0, 1f
+ ldmia r0, {r3-r5, r7}
+ sub r3, r0, r3 @ PHYS_OFFSET - PAGE_OFFSET
+ add r4, r4, r3 @ adjust table start address
+ add r5, r5, r3 @ adjust table end address
+ str r8, [r7, r3]! @ save computed PHYS_OFFSET to __pv_phys_offset
+ mov r6, r3, lsr #24 @ constant for add/sub instructions
+ teq r3, r6, lsl #24 @ must be 16MiB aligned
+ bne __error
+ str r6, [r7, #4] @ save to __pv_offset
+ b __fixup_a_pv_table
+ENDPROC(__fixup_pv_table)
+
+ .align
+1: .long .
+ .long __pv_table_begin
+ .long __pv_table_end
+2: .long __pv_phys_offset
+
+ .text
+__fixup_a_pv_table:
+ b 3f
+2: ldr ip, [r7, r3]
+ bic ip, ip, #0x000000ff
+ orr ip, ip, r6
+ str ip, [r7, r3]
+3: cmp r4, r5
+ ldrcc r7, [r4], #4 @ use branch for delay slot
+ bcc 2b
+ mov pc, lr
+ENDPROC(__fixup_a_pv_table)
+
+ENTRY(fixup_pv_table)
+ stmfd sp!, {r4 - r7, lr}
+ ldr r2, 2f @ get address of __pv_phys_offset
+ mov r3, #0 @ no offset
+ mov r4, r0 @ r0 = table start
+ add r5, r0, r1 @ r1 = table size
+ ldr r6, [r2, #4] @ get __pv_offset
+ bl __fixup_a_pv_table
+ ldmfd sp!, {r4 - r7, pc}
+ENDPROC(fixup_pv_table)
+
+ .align
+2: .long __pv_phys_offset
+
+ .data
+ .globl __pv_phys_offset
+ .type __pv_phys_offset, %object
+__pv_phys_offset:
+ .long 0
+ .size __pv_phys_offset, . - __pv_phys_offset
+__pv_offset:
+ .long 0
+#endif
+
#include "head-common.S"
diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c
index 2cfe816..c5679f6 100644
--- a/arch/arm/kernel/module.c
+++ b/arch/arm/kernel/module.c
@@ -268,12 +268,28 @@
const Elf_Shdr *txt_sec;
};
+static const Elf_Shdr *find_mod_section(const Elf32_Ehdr *hdr,
+ const Elf_Shdr *sechdrs, const char *name)
+{
+ const Elf_Shdr *s, *se;
+ const char *secstrs = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
+
+ for (s = sechdrs, se = sechdrs + hdr->e_shnum; s < se; s++)
+ if (strcmp(name, secstrs + s->sh_name) == 0)
+ return s;
+
+ return NULL;
+}
+
+extern void fixup_pv_table(const void *, unsigned long);
+
int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs,
struct module *mod)
{
+ const Elf_Shdr *s = NULL;
#ifdef CONFIG_ARM_UNWIND
const char *secstrs = (void *)hdr + sechdrs[hdr->e_shstrndx].sh_offset;
- const Elf_Shdr *s, *sechdrs_end = sechdrs + hdr->e_shnum;
+ const Elf_Shdr *sechdrs_end = sechdrs + hdr->e_shnum;
struct mod_unwind_map maps[ARM_SEC_MAX];
int i;
@@ -315,6 +331,11 @@
maps[i].txt_sec->sh_addr,
maps[i].txt_sec->sh_size);
#endif
+#ifdef CONFIG_ARM_PATCH_PHYS_VIRT
+ s = find_mod_section(hdr, sechdrs, ".pv_table");
+ if (s)
+ fixup_pv_table((void *)s->sh_addr, s->sh_size);
+#endif
return 0;
}
diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 86b66f3..45b5651 100644
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -57,6 +57,10 @@
__smpalt_end = .;
#endif
+ __pv_table_begin = .;
+ *(.pv_table)
+ __pv_table_end = .;
+
INIT_SETUP(16)
INIT_CALLS