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Message-ID: <52600488.3090401@gmail.com>
Date: Thu, 17 Oct 2013 23:38:48 +0800
From: Jiang Liu <liuj97@...il.com>
To: Will Deacon <will.deacon@....com>
CC: Steven Rostedt <rostedt@...dmis.org>,
Catalin Marinas <Catalin.Marinas@....com>,
Sandeepa Prabhu <sandeepa.prabhu@...aro.org>,
Jiang Liu <jiang.liu@...wei.com>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
tixy@...aro.org
Subject: Re: [PATCH v4 2/7] arm64: introduce interfaces to hotpatch kernel
and module code
On 10/17/2013 07:38 PM, Will Deacon wrote:
> [adding Tixy for stop_machine() question below]
>
> On Thu, Oct 17, 2013 at 07:19:35AM +0100, Jiang Liu wrote:
>> From: Jiang Liu <jiang.liu@...wei.com>
>>
>> Introduce three interfaces to patch kernel and module code:
>> aarch64_insn_patch_text_nosync():
>> patch code without synchronization, it's caller's responsibility
>> to synchronize all CPUs if needed.
>> aarch64_insn_patch_text_sync():
>> patch code and always synchronize with stop_machine()
>> aarch64_insn_patch_text():
>> patch code and synchronize with stop_machine() if needed
>>
>> Signed-off-by: Jiang Liu <jiang.liu@...wei.com>
>> Cc: Jiang Liu <liuj97@...il.com>
>> ---
>> arch/arm64/include/asm/insn.h | 24 +++++++++++++-
>> arch/arm64/kernel/insn.c | 77 +++++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 100 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/arm64/include/asm/insn.h b/arch/arm64/include/asm/insn.h
>> index 6190016..fc439b9 100644
>> --- a/arch/arm64/include/asm/insn.h
>> +++ b/arch/arm64/include/asm/insn.h
>> @@ -60,8 +60,30 @@ __AARCH64_INSN_FUNCS(nop, 0xFFFFFFFF, 0xD503201F)
>>
>> #undef __AARCH64_INSN_FUNCS
>>
>> -enum aarch64_insn_encoding_class aarch64_get_insn_class(u32 insn);
>> +/*
>> + * In ARMv8-A, A64 instructions have a fixed length of 32 bits and are always
>> + * little-endian. On the other hand, SCTLR_EL1.EE (bit 25, Exception Endianness)
>> + * flag controls endianness for EL1 explicit data accesses and stage 1
>> + * translation table walks as below:
>> + * 0: little-endian
>> + * 1: big-endian
>> + * So need to handle endianness when patching kernel code.
>> + */
>
> You can delete this comment now that we're using the helpers...
>
>> +static __always_inline u32 aarch64_insn_read(void *addr)
>> +{
>> + return le32_to_cpu(*(u32 *)addr);
>> +}
>>
>> +static __always_inline void aarch64_insn_write(void *addr, u32 insn)
>> +{
>> + *(u32 *)addr = cpu_to_le32(insn);
>> +}
>
> ... then just inline these calls directly.
>
>> +enum aarch64_insn_encoding_class aarch64_get_insn_class(u32 insn);
>> bool aarch64_insn_hotpatch_safe(u32 old_insn, u32 new_insn);
>>
>> +int aarch64_insn_patch_text_nosync(void *addrs[], u32 insns[], int cnt);
>> +int aarch64_insn_patch_text_sync(void *addrs[], u32 insns[], int cnt);
>> +int aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt);
>> +
>> #endif /* _ASM_ARM64_INSN_H */
>> diff --git a/arch/arm64/kernel/insn.c b/arch/arm64/kernel/insn.c
>> index 1c501f3..8dd5fbe 100644
>> --- a/arch/arm64/kernel/insn.c
>> +++ b/arch/arm64/kernel/insn.c
>> @@ -16,6 +16,9 @@
>> */
>> #include <linux/compiler.h>
>> #include <linux/kernel.h>
>> +#include <linux/smp.h>
>> +#include <linux/stop_machine.h>
>> +#include <asm/cacheflush.h>
>> #include <asm/insn.h>
>>
>> static int aarch64_insn_encoding_cls[] = {
>> @@ -70,3 +73,77 @@ bool __kprobes aarch64_insn_hotpatch_safe(u32 old_insn, u32 new_insn)
>> return __aarch64_insn_hotpatch_safe(old_insn) &&
>> __aarch64_insn_hotpatch_safe(new_insn);
>> }
>> +
>> +int __kprobes aarch64_insn_patch_text_nosync(void *addrs[], u32 insns[],
>> + int cnt)
>> +{
>> + int i;
>> + u32 *tp;
>> +
>> + if (cnt <= 0)
>> + return -EINVAL;
>
> Isn't cnt always 1 for the _nosync patching? Can you just drop the argument
> and simplify this code? Patching a sequence without syncing is always racy.
Will drop the third parameter and simplify the code.
>
>> + for (i = 0; i < cnt; i++) {
>> + tp = addrs[i];
>> + /* A64 instructions must be word aligned */
>> + if ((uintptr_t)tp & 0x3)
>> + return -EINVAL;
>> + aarch64_insn_write(tp, insns[i]);
>> + flush_icache_range((uintptr_t)tp, (uintptr_t)tp + sizeof(u32));
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +struct aarch64_insn_patch {
>> + void **text_addrs;
>> + u32 *new_insns;
>> + int insn_cnt;
>> +};
>> +
>> +static int __kprobes aarch64_insn_patch_text_cb(void *arg)
>> +{
>> + struct aarch64_insn_patch *pp = arg;
>> +
>> + return aarch64_insn_patch_text_nosync(pp->text_addrs, pp->new_insns,
>> + pp->insn_cnt);
>> +}
>> +
>> +int __kprobes aarch64_insn_patch_text_sync(void *addrs[], u32 insns[], int cnt)
>> +{
>> + struct aarch64_insn_patch patch = {
>> + .text_addrs = addrs,
>> + .new_insns = insns,
>> + .insn_cnt = cnt,
>> + };
>> +
>> + if (cnt <= 0)
>> + return -EINVAL;
>> +
>> + /*
>> + * Execute __aarch64_insn_patch_text() on every online CPU,
>> + * which ensure serialization among all online CPUs.
>> + */
>> + return stop_machine(aarch64_insn_patch_text_cb, &patch, NULL);
>> +}
>
> Whoa, whoa, whoa! The comment here is wrong -- we only run the patching on
> *one* CPU, which is the right thing to do. However, the arch/arm/ call to
> stop_machine in kprobes does actually run the patching code on *all* the
> online cores (including the cache flushing!). I think this is to work around
> cores without hardware cache maintenance broadcasting, but that could easily
> be called out specially (like we do in patch.c) and the flushing could be
> separated from the patching too.
>
>> +int __kprobes aarch64_insn_patch_text(void *addrs[], u32 insns[], int cnt)
>> +{
>> + int ret;
>> +
>> + if (cnt == 1 && aarch64_insn_hotpatch_safe(aarch64_insn_read(addrs[0]),
>> + insns[0])) {
>
> You could make aarch64_insn_hotpatch_safe take the cnt parameter and return
> false if cnt != 1.
>
>> + /*
>> + * It doesn't guarantee all CPUs see the new instruction
>
> "It"? You mean the ARMv8 architecture?
Yes, I mean ARMv8 architecture.
>
> Will
>
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