Use an atomic update for immediate values. Signed-off-by: Mathieu Desnoyers CC: Rusty Russell CC: Christoph Hellwig CC: Paul Mackerras --- arch/powerpc/kernel/Makefile | 1 arch/powerpc/kernel/immediate.c | 73 ++++++++++++++++++++++++++++++++++++++++ include/asm-powerpc/immediate.h | 18 +++++++++ 3 files changed, 92 insertions(+) Index: linux-2.6-lttng/arch/powerpc/kernel/immediate.c =================================================================== --- /dev/null 1970-01-01 00:00:00.000000000 +0000 +++ linux-2.6-lttng/arch/powerpc/kernel/immediate.c 2007-12-20 20:52:27.000000000 -0500 @@ -0,0 +1,73 @@ +/* + * Powerpc optimized immediate values enabling/disabling. + * + * Mathieu Desnoyers + */ + +#include +#include +#include +#include +#include +#include + +#define LI_OPCODE_LEN 2 + +/** + * arch_imv_update - update one immediate value + * @imv: pointer of type const struct __imv to update + * @early: early boot (1), normal (0) + * + * Update one immediate value. Must be called with imv_mutex held. + */ +int arch_imv_update(const struct __imv *imv, int early) +{ +#ifdef CONFIG_KPROBES + kprobe_opcode_t *insn; + /* + * Fail if a kprobe has been set on this instruction. + * (TODO: we could eventually do better and modify all the (possibly + * nested) kprobes for this site if kprobes had an API for this. + */ + switch (imv->size) { + case 1: /* The uint8_t points to the 3rd byte of the + * instruction */ + insn = (void *)(imv->imv - 1 - LI_OPCODE_LEN); + break; + case 2: insn = (void *)(imv->imv - LI_OPCODE_LEN); + break; + default: + return -EINVAL; + } + + if (unlikely(!early && *insn == BREAKPOINT_INSTRUCTION)) { + printk(KERN_WARNING "Immediate value in conflict with kprobe. " + "Variable at %p, " + "instruction at %p, size %lu\n", + (void *)imv->imv, + (void *)imv->var, imv->size); + return -EBUSY; + } +#endif + + /* + * If the variable and the instruction have the same value, there is + * nothing to do. + */ + switch (imv->size) { + case 1: if (*(uint8_t *)imv->imv + == *(uint8_t *)imv->var) + return 0; + break; + case 2: if (*(uint16_t *)imv->imv + == *(uint16_t *)imv->var) + return 0; + break; + default:return -EINVAL; + } + memcpy((void *)imv->imv, (void *)imv->var, + imv->size); + flush_icache_range(imv->imv, + imv->imv + imv->size); + return 0; +} Index: linux-2.6-lttng/include/asm-powerpc/immediate.h =================================================================== --- linux-2.6-lttng.orig/include/asm-powerpc/immediate.h 2007-12-20 20:52:20.000000000 -0500 +++ linux-2.6-lttng/include/asm-powerpc/immediate.h 2007-12-20 20:52:27.000000000 -0500 @@ -12,6 +12,16 @@ #include +struct __imv { + unsigned long var; /* Identifier variable of the immediate value */ + unsigned long imv; /* + * Pointer to the memory location that holds + * the immediate value within the load immediate + * instruction. + */ + unsigned char size; /* Type size. */ +} __attribute__ ((packed)); + /** * imv_read - read immediate variable * @name: immediate value name @@ -19,6 +29,11 @@ * Reads the value of @name. * Optimized version of the immediate. * Do not use in __init and __exit functions. Use _imv_read() instead. + * Makes sure the 2 bytes update will be atomic by aligning the immediate + * value. Use a normal memory read for the 4 bytes immediate because there is no + * way to atomically update it without using a seqlock read side, which would + * cost more in term of total i-cache and d-cache space than a simple memory + * read. */ #define imv_read(name) \ ({ \ @@ -40,6 +55,7 @@ PPC_LONG "%c1, ((1f)-2)\n\t" \ ".byte 2\n\t" \ ".previous\n\t" \ + ".align 2\n\t" \ "li %0,0\n\t" \ "1:\n\t" \ : "=r" (value) \ @@ -52,4 +68,6 @@ value; \ }) +extern int arch_imv_update(const struct __imv *imv, int early); + #endif /* _ASM_POWERPC_IMMEDIATE_H */ Index: linux-2.6-lttng/arch/powerpc/kernel/Makefile =================================================================== --- linux-2.6-lttng.orig/arch/powerpc/kernel/Makefile 2007-12-20 20:52:20.000000000 -0500 +++ linux-2.6-lttng/arch/powerpc/kernel/Makefile 2007-12-20 20:52:27.000000000 -0500 @@ -91,3 +91,4 @@ obj-$(CONFIG_PPC64) += $(obj64-y) extra-$(CONFIG_PPC_FPU) += fpu.o extra-$(CONFIG_PPC64) += entry_64.o +obj-$(CONFIG_IMMEDIATE) += immediate.o -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/