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Date: Sat, 11 Aug 2012 23:03:09 -0400 (EDT)
From: Nicolas Pitre <nicolas.pitre@...aro.org>
To: Cyril Chemparathy <cyril@...com>
cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
Arnd Bergmann <arnd@...db.de>,
Catalin Marinas <catalin.marinas@....com>,
Grant Likely <grant.likely@...retlab.ca>,
Russell King - ARM Linux <linux@....linux.org.uk>,
Will Deacon <will.deacon@....com>
Subject: Re: [PATCH v2 03/22] ARM: use late patch framework for phys-virt
patching
On Fri, 10 Aug 2012, Cyril Chemparathy wrote:
> This patch replaces the original physical offset patching implementation
> with one that uses the newly added patching framework. In the process, we now
> unconditionally initialize the __pv_phys_offset and __pv_offset globals in the
> head.S code.
This last sentence is now wrong.
[...]
> diff --git a/arch/arm/include/asm/memory.h b/arch/arm/include/asm/memory.h
> index e965f1b..3d93779 100644
> --- a/arch/arm/include/asm/memory.h
> +++ b/arch/arm/include/asm/memory.h
> @@ -18,6 +18,8 @@
> #include <linux/types.h>
> #include <linux/sizes.h>
>
> +#include <asm/runtime-patch.h>
> +
> #ifdef CONFIG_NEED_MACH_MEMORY_H
> #include <mach/memory.h>
> #endif
> @@ -151,35 +153,21 @@
> #ifndef __virt_to_phys
> #ifdef CONFIG_ARM_PATCH_PHYS_VIRT
>
> -/*
> - * Constants used to force the right instruction encodings and shifts
> - * so that all we need to do is modify the 8-bit constant field.
> - */
> -#define __PV_BITS_31_24 0x81000000
> -
> -extern unsigned long __pv_phys_offset;
> -#define PHYS_OFFSET __pv_phys_offset
> -
> -#define __pv_stub(from,to,instr,type) \
> - __asm__("@ __pv_stub\n" \
> - "1: " instr " %0, %1, %2\n" \
> - " .pushsection .pv_table,\"a\"\n" \
> - " .long 1b\n" \
> - " .popsection\n" \
> - : "=r" (to) \
> - : "r" (from), "I" (type))
> +extern unsigned long __pv_offset;
> +extern unsigned long __pv_phys_offset;
> +#define PHYS_OFFSET __virt_to_phys(PAGE_OFFSET)
What was wrong with the former PHYS_OFFSET = __pv_phys_offset ?
If you really want to have it optimized at run time, you could simply
use your new stub to patch a mov instruction instead of going through
__virt_to_phys which uses and add on top of a constant.
> static inline unsigned long __virt_to_phys(unsigned long x)
> {
> unsigned long t;
> - __pv_stub(x, t, "add", __PV_BITS_31_24);
> + early_patch_imm8("add", t, x, __pv_offset, 0);
> return t;
> }
>
> static inline unsigned long __phys_to_virt(unsigned long x)
> {
> unsigned long t;
> - __pv_stub(x, t, "sub", __PV_BITS_31_24);
> + early_patch_imm8("sub", t, x, __pv_offset, 0);
> return t;
> }
> #else
> diff --git a/arch/arm/kernel/armksyms.c b/arch/arm/kernel/armksyms.c
> index 60d3b73..6b388f8 100644
> --- a/arch/arm/kernel/armksyms.c
> +++ b/arch/arm/kernel/armksyms.c
> @@ -152,7 +152,3 @@ EXPORT_SYMBOL(mcount);
> #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 3db960e..69a3c09 100644
> --- a/arch/arm/kernel/head.S
> +++ b/arch/arm/kernel/head.S
> @@ -117,7 +117,7 @@ ENTRY(stext)
> bl __fixup_smp
> #endif
> #ifdef CONFIG_ARM_PATCH_PHYS_VIRT
> - bl __fixup_pv_table
> + bl __fixup_pv_offsets
> #endif
> bl __create_page_tables
>
> @@ -511,92 +511,29 @@ ENDPROC(fixup_smp)
>
> #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'.
> +/*
> + * __fixup_pv_offsets - update __pv_offset and __pv_phys_offset based on the
> + * runtime location of the kernel.
> */
> __HEAD
> -__fixup_pv_table:
> +__fixup_pv_offsets:
> adr r0, 1f
> - ldmia r0, {r3-r5, r7}
> + ldmia r0, {r3-r6}
> sub r3, r0, r3 @ PHYS_OFFSET - PAGE_OFFSET
> - add r4, r4, r3 @ adjust table start address
> - add r5, r5, r3 @ adjust table end address
> - add r7, r7, r3 @ adjust __pv_phys_offset address
> - str r8, [r7] @ 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
> -THUMB( it ne @ cross section branch )
> - bne __error
> - str r6, [r7, #4] @ save to __pv_offset
> - b __fixup_a_pv_table
> -ENDPROC(__fixup_pv_table)
> + add r4, r4, r3 @ virt_to_phys(__pv_phys_offset)
> + add r5, r5, r3 @ virt_to_phys(__pv_offset)
> + add r6, r6, r3 @ virt_to_phys(PAGE_OFFSET) = PHYS_OFFSET
> + str r6, [r4] @ save __pv_phys_offset
> + str r3, [r5] @ save __pv_offset
> + mov pc, lr
> +ENDPROC(__fixup_pv_offsets)
>
> .align
> 1: .long .
> - .long __pv_table_begin
> - .long __pv_table_end
> -2: .long __pv_phys_offset
> -
> - .text
> -__fixup_a_pv_table:
> -#ifdef CONFIG_THUMB2_KERNEL
> - lsls r6, #24
> - beq 2f
> - clz r7, r6
> - lsr r6, #24
> - lsl r6, r7
> - bic r6, #0x0080
> - lsrs r7, #1
> - orrcs r6, #0x0080
> - orr r6, r6, r7, lsl #12
> - orr r6, #0x4000
> - b 2f
> -1: add r7, r3
> - ldrh ip, [r7, #2]
> - and ip, 0x8f00
> - orr ip, r6 @ mask in offset bits 31-24
> - strh ip, [r7, #2]
> -2: cmp r4, r5
> - ldrcc r7, [r4], #4 @ use branch for delay slot
> - bcc 1b
> - bx lr
> -#else
> - b 2f
> -1: ldr ip, [r7, r3]
> - bic ip, ip, #0x000000ff
> - orr ip, ip, r6 @ mask in offset bits 31-24
> - str ip, [r7, r3]
> -2: cmp r4, r5
> - ldrcc r7, [r4], #4 @ use branch for delay slot
> - bcc 1b
> - mov pc, lr
> + .long __pv_phys_offset
> + .long __pv_offset
> + .long PAGE_OFFSET
> #endif
> -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 dcebf80..ac13dd5 100644
> --- a/arch/arm/kernel/module.c
> +++ b/arch/arm/kernel/module.c
> @@ -317,11 +317,6 @@ int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs,
> 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
> s = find_mod_section(hdr, sechdrs, ".runtime.patch.table");
> if (s)
> runtime_patch((void *)s->sh_addr, s->sh_size);
I missed this in the previous patch, but could you fail the module
loading by returning an error if runtime_patch() fails? That would take
care of not accepting modules that might have been compiled with future
runtime patching extensions that are not yet supported in an earlier
kernel.
You also should remove the MODULE_ARCH_VERMAGIC_P2V definitions now that
the corresponding code is no longer there.
Nicolas
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