From: Pu Lehui <[email protected]>
Implement bpf_arch_text_poke for RV64. For call scenario,
ftrace framework reserve 4 nops for RV64 kernel function
as function entry, and use auipc+jalr instructions to call
kernel or module functions. However, since the auipc+jalr
call instructions is non-atomic operation, we need to use
stop-machine to make sure instruction patching in atomic
context. As for jump scenario, since we only jump inside
the trampoline, a jal instruction is sufficient.
Signed-off-by: Pu Lehui <[email protected]>
---
arch/riscv/net/bpf_jit.h | 5 ++
arch/riscv/net/bpf_jit_comp64.c | 131 +++++++++++++++++++++++++++++++-
2 files changed, 134 insertions(+), 2 deletions(-)
diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
index d926e0f7ef57..bf9802a63061 100644
--- a/arch/riscv/net/bpf_jit.h
+++ b/arch/riscv/net/bpf_jit.h
@@ -573,6 +573,11 @@ static inline u32 rv_fence(u8 pred, u8 succ)
return rv_i_insn(imm11_0, 0, 0, 0, 0xf);
}
+static inline u32 rv_nop(void)
+{
+ return rv_i_insn(0, 0, 0, 0, 0x13);
+}
+
/* RVC instrutions. */
static inline u16 rvc_addi4spn(u8 rd, u32 imm10)
diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
index bf4721a99a09..fa8b03c52463 100644
--- a/arch/riscv/net/bpf_jit_comp64.c
+++ b/arch/riscv/net/bpf_jit_comp64.c
@@ -8,6 +8,8 @@
#include <linux/bitfield.h>
#include <linux/bpf.h>
#include <linux/filter.h>
+#include <linux/memory.h>
+#include <linux/stop_machine.h>
#include "bpf_jit.h"
#define RV_REG_TCC RV_REG_A6
@@ -238,7 +240,7 @@ static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
if (!is_tail_call)
emit_mv(RV_REG_A0, RV_REG_A5, ctx);
emit_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA,
- is_tail_call ? 4 : 0, /* skip TCC init */
+ is_tail_call ? 20 : 0, /* skip reserved nops and TCC init */
ctx);
}
@@ -615,6 +617,127 @@ static int add_exception_handler(const struct bpf_insn *insn,
return 0;
}
+struct text_poke_args {
+ void *addr;
+ const void *insns;
+ size_t len;
+ atomic_t cpu_count;
+};
+
+static int do_text_poke(void *data)
+{
+ int ret = 0;
+ struct text_poke_args *patch = data;
+
+ if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
+ ret = patch_text_nosync(patch->addr, patch->insns, patch->len);
+ atomic_inc(&patch->cpu_count);
+ } else {
+ while (atomic_read(&patch->cpu_count) <= num_online_cpus())
+ cpu_relax();
+ smp_mb();
+ }
+
+ return ret;
+}
+
+static int bpf_text_poke_stop_machine(void *addr, const void *insns, size_t len)
+{
+ struct text_poke_args patch = {
+ .addr = addr,
+ .insns = insns,
+ .len = len,
+ .cpu_count = ATOMIC_INIT(0),
+ };
+
+ return stop_machine(do_text_poke, &patch, cpu_online_mask);
+}
+
+static int gen_call_or_nops(void *target, void *ip, u32 *insns)
+{
+ int i, ret;
+ s64 rvoff;
+ struct rv_jit_context ctx;
+
+ ctx.ninsns = 0;
+ ctx.insns = (u16 *)insns;
+
+ if (!target) {
+ for (i = 0; i < 4; i++)
+ emit(rv_nop(), &ctx);
+ return 0;
+ }
+
+ rvoff = (s64)(target - ip);
+ emit(rv_sd(RV_REG_SP, -8, RV_REG_RA), &ctx);
+ ret = emit_jump_and_link(RV_REG_RA, rvoff, false, &ctx);
+ if (ret)
+ return ret;
+ emit(rv_ld(RV_REG_RA, -8, RV_REG_SP), &ctx);
+
+ return 0;
+
+}
+
+static int bpf_text_poke_call(void *ip, void *old_addr, void *new_addr)
+{
+ int ret;
+ u32 old_insns[4], new_insns[4];
+
+ ret = gen_call_or_nops(old_addr, ip + 4, old_insns);
+ if (ret)
+ return ret;
+
+ ret = gen_call_or_nops(new_addr, ip + 4, new_insns);
+ if (ret)
+ return ret;
+
+ mutex_lock(&text_mutex);
+ if (memcmp(ip, old_insns, sizeof(old_insns))) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ if (memcmp(ip, new_insns, sizeof(new_insns)))
+ ret = bpf_text_poke_stop_machine(ip, new_insns, sizeof(new_insns));
+out:
+ mutex_unlock(&text_mutex);
+ return ret;
+}
+
+static int bpf_text_poke_jump(void *ip, void *old_addr, void *new_addr)
+{
+ int ret;
+ u32 old_insn, new_insn;
+
+ old_insn = old_addr ? rv_jal(RV_REG_ZERO, (s64)(old_addr - ip) >> 1) : rv_nop();
+ new_insn = new_addr ? rv_jal(RV_REG_ZERO, (s64)(new_addr - ip) >> 1) : rv_nop();
+
+ mutex_lock(&text_mutex);
+ if (memcmp(ip, &old_insn, sizeof(old_insn))) {
+ ret = -EFAULT;
+ goto out;
+ }
+
+ if (memcmp(ip, &new_insn, sizeof(new_insn)))
+ ret = patch_text_nosync(ip, &new_insn, sizeof(new_insn));
+out:
+ mutex_unlock(&text_mutex);
+ return ret;
+}
+
+int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
+ void *old_addr, void *new_addr)
+{
+ if (!is_kernel_text((unsigned long)ip) &&
+ !is_bpf_text_address((unsigned long)ip))
+ return -ENOTSUPP;
+
+ return poke_type == BPF_MOD_CALL ?
+ bpf_text_poke_call(ip, old_addr, new_addr) :
+ bpf_text_poke_jump(ip, old_addr, new_addr);
+}
+
int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
bool extra_pass)
{
@@ -1266,7 +1389,7 @@ int bpf_jit_emit_insn(const struct bpf_insn *insn, struct rv_jit_context *ctx,
void bpf_jit_build_prologue(struct rv_jit_context *ctx)
{
- int stack_adjust = 0, store_offset, bpf_stack_adjust;
+ int i, stack_adjust = 0, store_offset, bpf_stack_adjust;
bool is_main_prog = ctx->prog->aux->func_idx == 0;
bpf_stack_adjust = round_up(ctx->prog->aux->stack_depth, 16);
@@ -1294,6 +1417,10 @@ void bpf_jit_build_prologue(struct rv_jit_context *ctx)
store_offset = stack_adjust - 8;
+ /* reserve 4 nop insns */
+ for (i = 0; i < 4; i++)
+ emit(rv_nop(), ctx);
+
/* First instruction is always setting the tail-call-counter
* (TCC) register. This instruction is skipped for tail calls.
* Force using a 4-byte (non-compressed) instruction.
--
2.25.1
On 2022/12/20 11:00, Xu Kuohai wrote:
> On 12/20/2022 10:13 AM, Pu Lehui wrote:
>> From: Pu Lehui <[email protected]>
>>
>> Implement bpf_arch_text_poke for RV64. For call scenario,
>> ftrace framework reserve 4 nops for RV64 kernel function
>> as function entry, and use auipc+jalr instructions to call
>> kernel or module functions. However, since the auipc+jalr
>> call instructions is non-atomic operation, we need to use
>> stop-machine to make sure instruction patching in atomic
>> context. As for jump scenario, since we only jump inside
>> the trampoline, a jal instruction is sufficient.
>>
>> Signed-off-by: Pu Lehui <[email protected]>
>> ---
>> arch/riscv/net/bpf_jit.h | 5 ++
>> arch/riscv/net/bpf_jit_comp64.c | 131 +++++++++++++++++++++++++++++++-
>> 2 files changed, 134 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
>> index d926e0f7ef57..bf9802a63061 100644
>> --- a/arch/riscv/net/bpf_jit.h
>> +++ b/arch/riscv/net/bpf_jit.h
>> @@ -573,6 +573,11 @@ static inline u32 rv_fence(u8 pred, u8 succ)
>> return rv_i_insn(imm11_0, 0, 0, 0, 0xf);
>> }
>> +static inline u32 rv_nop(void)
>> +{
>> + return rv_i_insn(0, 0, 0, 0, 0x13);
>> +}
>> +
>> /* RVC instrutions. */
>> static inline u16 rvc_addi4spn(u8 rd, u32 imm10)
>> diff --git a/arch/riscv/net/bpf_jit_comp64.c
>> b/arch/riscv/net/bpf_jit_comp64.c
>> index bf4721a99a09..fa8b03c52463 100644
>> --- a/arch/riscv/net/bpf_jit_comp64.c
>> +++ b/arch/riscv/net/bpf_jit_comp64.c
>> @@ -8,6 +8,8 @@
>> #include <linux/bitfield.h>
>> #include <linux/bpf.h>
>> #include <linux/filter.h>
>> +#include <linux/memory.h>
>> +#include <linux/stop_machine.h>
>> #include "bpf_jit.h"
>> #define RV_REG_TCC RV_REG_A6
>> @@ -238,7 +240,7 @@ static void __build_epilogue(bool is_tail_call,
>> struct rv_jit_context *ctx)
>> if (!is_tail_call)
>> emit_mv(RV_REG_A0, RV_REG_A5, ctx);
>> emit_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA,
>> - is_tail_call ? 4 : 0, /* skip TCC init */
>> + is_tail_call ? 20 : 0, /* skip reserved nops and TCC init */
>> ctx);
>> }
>> @@ -615,6 +617,127 @@ static int add_exception_handler(const struct
>> bpf_insn *insn,
>> return 0;
>> }
>> +struct text_poke_args {
>> + void *addr;
>> + const void *insns;
>> + size_t len;
>> + atomic_t cpu_count;
>> +};
>> +
>> +static int do_text_poke(void *data)
>> +{
>> + int ret = 0;
>> + struct text_poke_args *patch = data;
>> +
>> + if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
>
> seems this sync is not needed, why not calling stop machine like this:
>
> stop_machine(do_text_poke, &patch, NULL);
>
I think both version should be ok. While the NULL version uses first cpu
as master to patch_text and the others touch nmi watchdog, this version
attempts to let other cpus enter cpu_relax to calm down, and let master
cpu owns system resources as possible.
>> + ret = patch_text_nosync(patch->addr, patch->insns, patch->len);
>> + atomic_inc(&patch->cpu_count);
>> + } else {
>> + while (atomic_read(&patch->cpu_count) <= num_online_cpus())
>> + cpu_relax();
>> + smp_mb();
>> + }
>> +
>> + return ret;
>> +}
>> +
>> +static int bpf_text_poke_stop_machine(void *addr, const void *insns,
>> size_t len)
>> +{
>> + struct text_poke_args patch = {
>> + .addr = addr,
>> + .insns = insns,
>> + .len = len,
>> + .cpu_count = ATOMIC_INIT(0),
>> + };
>> +
>> + return stop_machine(do_text_poke, &patch, cpu_online_mask);
>> +}
>> +
>> +static int gen_call_or_nops(void *target, void *ip, u32 *insns)
>> +{
>> + int i, ret;
>> + s64 rvoff;
>> + struct rv_jit_context ctx;
>> +
>> + ctx.ninsns = 0;
>> + ctx.insns = (u16 *)insns;
>> +
>> + if (!target) {
>> + for (i = 0; i < 4; i++)
>> + emit(rv_nop(), &ctx);
>> + return 0;
>> + }
>> +
>> + rvoff = (s64)(target - ip);
>> + emit(rv_sd(RV_REG_SP, -8, RV_REG_RA), &ctx);
>> + ret = emit_jump_and_link(RV_REG_RA, rvoff, false, &ctx);
>> + if (ret)
>> + return ret;
>> + emit(rv_ld(RV_REG_RA, -8, RV_REG_SP), &ctx);
>> +
>> + return 0;
>> +
>> +}
>> +
>> +static int bpf_text_poke_call(void *ip, void *old_addr, void *new_addr)
>> +{
>> + int ret;
>> + u32 old_insns[4], new_insns[4];
>> +
>> + ret = gen_call_or_nops(old_addr, ip + 4, old_insns);
>> + if (ret)
>> + return ret;
>> +
>> + ret = gen_call_or_nops(new_addr, ip + 4, new_insns);
>> + if (ret)
>> + return ret;
>> +
>> + mutex_lock(&text_mutex);
>> + if (memcmp(ip, old_insns, sizeof(old_insns))) {
>> + ret = -EFAULT;
>> + goto out;
>> + }
>> +
>> + if (memcmp(ip, new_insns, sizeof(new_insns)))
>> + ret = bpf_text_poke_stop_machine(ip, new_insns,
>> sizeof(new_insns));
>
> since there are 4 instructions being replaced, it is possible that
> serveral old instructions were already executed before stop machine.
>
Yes, there are unpredictable problems after stop machine in that
situation. In addition, probing stop machine sub-functions may lead to
loop nesting problems. And this is the current problem with riscv ftrace.
But the surprise was that Andy's work [1] was about to solve these
problems. We can synchronize changes in the future.
[1]
https://lore.kernel.org/linux-riscv/[email protected]
>> +out:
>> + mutex_unlock(&text_mutex);
>> + return ret;
>> +}
>> +
>> +static int bpf_text_poke_jump(void *ip, void *old_addr, void *new_addr)
>> +{
>> + int ret;
>> + u32 old_insn, new_insn;
>> +
>> + old_insn = old_addr ? rv_jal(RV_REG_ZERO, (s64)(old_addr - ip) >>
>> 1) : rv_nop();
>> + new_insn = new_addr ? rv_jal(RV_REG_ZERO, (s64)(new_addr - ip) >>
>> 1) : rv_nop();
>> +
>> + mutex_lock(&text_mutex);
>> + if (memcmp(ip, &old_insn, sizeof(old_insn))) {
>> + ret = -EFAULT;
>> + goto out;
>> + }
>> +
>> + if (memcmp(ip, &new_insn, sizeof(new_insn)))
>> + ret = patch_text_nosync(ip, &new_insn, sizeof(new_insn));
>> +out:
>> + mutex_unlock(&text_mutex);
>> + return ret;
>> +}
>> +
>> +int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
>> + void *old_addr, void *new_addr)
>> +{
>> + if (!is_kernel_text((unsigned long)ip) &&
>> + !is_bpf_text_address((unsigned long)ip))
>> + return -ENOTSUPP;
>> +
>> + return poke_type == BPF_MOD_CALL ?
>> + bpf_text_poke_call(ip, old_addr, new_addr) :
>> + bpf_text_poke_jump(ip, old_addr, new_addr);
>> +}
>> +
>> int bpf_jit_emit_insn(const struct bpf_insn *insn, struct
>> rv_jit_context *ctx,
>> bool extra_pass)
>> {
>> @@ -1266,7 +1389,7 @@ int bpf_jit_emit_insn(const struct bpf_insn
>> *insn, struct rv_jit_context *ctx,
>> void bpf_jit_build_prologue(struct rv_jit_context *ctx)
>> {
>> - int stack_adjust = 0, store_offset, bpf_stack_adjust;
>> + int i, stack_adjust = 0, store_offset, bpf_stack_adjust;
>> bool is_main_prog = ctx->prog->aux->func_idx == 0;
>> bpf_stack_adjust = round_up(ctx->prog->aux->stack_depth, 16);
>> @@ -1294,6 +1417,10 @@ void bpf_jit_build_prologue(struct
>> rv_jit_context *ctx)
>> store_offset = stack_adjust - 8;
>> + /* reserve 4 nop insns */
>> + for (i = 0; i < 4; i++)
>> + emit(rv_nop(), ctx);
>> +
>> /* First instruction is always setting the tail-call-counter
>> * (TCC) register. This instruction is skipped for tail calls.
>> * Force using a 4-byte (non-compressed) instruction.
Pu Lehui <[email protected]> writes:
> From: Pu Lehui <[email protected]>
>
> Implement bpf_arch_text_poke for RV64. For call scenario,
> ftrace framework reserve 4 nops for RV64 kernel function
> as function entry, and use auipc+jalr instructions to call
> kernel or module functions. However, since the auipc+jalr
> call instructions is non-atomic operation, we need to use
> stop-machine to make sure instruction patching in atomic
> context. As for jump scenario, since we only jump inside
> the trampoline, a jal instruction is sufficient.
Hmm, is that really true? More below!
>
> Signed-off-by: Pu Lehui <[email protected]>
> ---
> arch/riscv/net/bpf_jit.h | 5 ++
> arch/riscv/net/bpf_jit_comp64.c | 131 +++++++++++++++++++++++++++++++-
> 2 files changed, 134 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
> index d926e0f7ef57..bf9802a63061 100644
> --- a/arch/riscv/net/bpf_jit.h
> +++ b/arch/riscv/net/bpf_jit.h
> @@ -573,6 +573,11 @@ static inline u32 rv_fence(u8 pred, u8 succ)
> return rv_i_insn(imm11_0, 0, 0, 0, 0xf);
> }
>
> +static inline u32 rv_nop(void)
> +{
> + return rv_i_insn(0, 0, 0, 0, 0x13);
> +}
> +
> /* RVC instrutions. */
>
> static inline u16 rvc_addi4spn(u8 rd, u32 imm10)
> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
> index bf4721a99a09..fa8b03c52463 100644
> --- a/arch/riscv/net/bpf_jit_comp64.c
> +++ b/arch/riscv/net/bpf_jit_comp64.c
> @@ -8,6 +8,8 @@
> #include <linux/bitfield.h>
> #include <linux/bpf.h>
> #include <linux/filter.h>
> +#include <linux/memory.h>
> +#include <linux/stop_machine.h>
> #include "bpf_jit.h"
>
> #define RV_REG_TCC RV_REG_A6
> @@ -238,7 +240,7 @@ static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
> if (!is_tail_call)
> emit_mv(RV_REG_A0, RV_REG_A5, ctx);
> emit_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA,
> - is_tail_call ? 4 : 0, /* skip TCC init */
> + is_tail_call ? 20 : 0, /* skip reserved nops and TCC init */
> ctx);
> }
>
> @@ -615,6 +617,127 @@ static int add_exception_handler(const struct bpf_insn *insn,
> return 0;
> }
>
> +struct text_poke_args {
> + void *addr;
> + const void *insns;
> + size_t len;
> + atomic_t cpu_count;
> +};
> +
> +static int do_text_poke(void *data)
> +{
> + int ret = 0;
> + struct text_poke_args *patch = data;
> +
> + if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
> + ret = patch_text_nosync(patch->addr, patch->insns, patch->len);
> + atomic_inc(&patch->cpu_count);
> + } else {
> + while (atomic_read(&patch->cpu_count) <= num_online_cpus())
> + cpu_relax();
> + smp_mb();
> + }
> +
> + return ret;
> +}
> +
> +static int bpf_text_poke_stop_machine(void *addr, const void *insns, size_t len)
> +{
> + struct text_poke_args patch = {
> + .addr = addr,
> + .insns = insns,
> + .len = len,
> + .cpu_count = ATOMIC_INIT(0),
> + };
> +
> + return stop_machine(do_text_poke, &patch, cpu_online_mask);
> +}
> +
> +static int gen_call_or_nops(void *target, void *ip, u32 *insns)
> +{
> + int i, ret;
> + s64 rvoff;
> + struct rv_jit_context ctx;
> +
> + ctx.ninsns = 0;
> + ctx.insns = (u16 *)insns;
> +
> + if (!target) {
> + for (i = 0; i < 4; i++)
> + emit(rv_nop(), &ctx);
> + return 0;
> + }
> +
> + rvoff = (s64)(target - ip);
> + emit(rv_sd(RV_REG_SP, -8, RV_REG_RA), &ctx);
> + ret = emit_jump_and_link(RV_REG_RA, rvoff, false, &ctx);
> + if (ret)
> + return ret;
> + emit(rv_ld(RV_REG_RA, -8, RV_REG_SP), &ctx);
> +
> + return 0;
> +
> +}
> +
> +static int bpf_text_poke_call(void *ip, void *old_addr, void *new_addr)
> +{
> + int ret;
> + u32 old_insns[4], new_insns[4];
> +
> + ret = gen_call_or_nops(old_addr, ip + 4, old_insns);
> + if (ret)
> + return ret;
> +
> + ret = gen_call_or_nops(new_addr, ip + 4, new_insns);
> + if (ret)
> + return ret;
> +
> + mutex_lock(&text_mutex);
> + if (memcmp(ip, old_insns, sizeof(old_insns))) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + if (memcmp(ip, new_insns, sizeof(new_insns)))
> + ret = bpf_text_poke_stop_machine(ip, new_insns,
> sizeof(new_insns));
I'd rather see that you added a patch_text variant to
arch/riscv/kernel/patch.c (something like your
bpf_text_poke_stop_machine()), and use that here. Might be other users
of that as well -- Andy's ftrace patch maybe? :-)
> +out:
> + mutex_unlock(&text_mutex);
> + return ret;
> +}
> +
> +static int bpf_text_poke_jump(void *ip, void *old_addr, void *new_addr)
> +{
> + int ret;
> + u32 old_insn, new_insn;
> +
> + old_insn = old_addr ? rv_jal(RV_REG_ZERO, (s64)(old_addr - ip) >> 1) : rv_nop();
> + new_insn = new_addr ? rv_jal(RV_REG_ZERO, (s64)(new_addr - ip) >> 1) : rv_nop();
> +
> + mutex_lock(&text_mutex);
> + if (memcmp(ip, &old_insn, sizeof(old_insn))) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + if (memcmp(ip, &new_insn, sizeof(new_insn)))
> + ret = patch_text_nosync(ip, &new_insn, sizeof(new_insn));
> +out:
> + mutex_unlock(&text_mutex);
> + return ret;
> +}
> +
> +int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
> + void *old_addr, void *new_addr)
AFAIU there's nothing in the bpf_arch_text_poke() API that say that
BPF_MOD_JUMP is jumps within the trampoline. That is one usage, but not
the only one. In general, the jal might not have enough reach.
I believe that this needs to be an auipc/jalr pair similar to
BPF_MOD_CALL (w/o linked register).
And again, thanks for working on the RV trampoline!
Björn
On 2023/1/4 2:12, Björn Töpel wrote:
> Pu Lehui <[email protected]> writes:
>
>> From: Pu Lehui <[email protected]>
>>
>> Implement bpf_arch_text_poke for RV64. For call scenario,
>> ftrace framework reserve 4 nops for RV64 kernel function
>> as function entry, and use auipc+jalr instructions to call
>> kernel or module functions. However, since the auipc+jalr
>> call instructions is non-atomic operation, we need to use
>> stop-machine to make sure instruction patching in atomic
>> context. As for jump scenario, since we only jump inside
>> the trampoline, a jal instruction is sufficient.
>
> Hmm, is that really true? More below!
>
>>
>> Signed-off-by: Pu Lehui <[email protected]>
>> ---
>> arch/riscv/net/bpf_jit.h | 5 ++
>> arch/riscv/net/bpf_jit_comp64.c | 131 +++++++++++++++++++++++++++++++-
>> 2 files changed, 134 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/riscv/net/bpf_jit.h b/arch/riscv/net/bpf_jit.h
>> index d926e0f7ef57..bf9802a63061 100644
>> --- a/arch/riscv/net/bpf_jit.h
>> +++ b/arch/riscv/net/bpf_jit.h
>> @@ -573,6 +573,11 @@ static inline u32 rv_fence(u8 pred, u8 succ)
>> return rv_i_insn(imm11_0, 0, 0, 0, 0xf);
>> }
>>
>> +static inline u32 rv_nop(void)
>> +{
>> + return rv_i_insn(0, 0, 0, 0, 0x13);
>> +}
>> +
>> /* RVC instrutions. */
>>
>> static inline u16 rvc_addi4spn(u8 rd, u32 imm10)
>> diff --git a/arch/riscv/net/bpf_jit_comp64.c b/arch/riscv/net/bpf_jit_comp64.c
>> index bf4721a99a09..fa8b03c52463 100644
>> --- a/arch/riscv/net/bpf_jit_comp64.c
>> +++ b/arch/riscv/net/bpf_jit_comp64.c
>> @@ -8,6 +8,8 @@
>> #include <linux/bitfield.h>
>> #include <linux/bpf.h>
>> #include <linux/filter.h>
>> +#include <linux/memory.h>
>> +#include <linux/stop_machine.h>
>> #include "bpf_jit.h"
>>
>> #define RV_REG_TCC RV_REG_A6
>> @@ -238,7 +240,7 @@ static void __build_epilogue(bool is_tail_call, struct rv_jit_context *ctx)
>> if (!is_tail_call)
>> emit_mv(RV_REG_A0, RV_REG_A5, ctx);
>> emit_jalr(RV_REG_ZERO, is_tail_call ? RV_REG_T3 : RV_REG_RA,
>> - is_tail_call ? 4 : 0, /* skip TCC init */
>> + is_tail_call ? 20 : 0, /* skip reserved nops and TCC init */
>> ctx);
>> }
>>
>> @@ -615,6 +617,127 @@ static int add_exception_handler(const struct bpf_insn *insn,
>> return 0;
>> }
>>
>> +struct text_poke_args {
>> + void *addr;
>> + const void *insns;
>> + size_t len;
>> + atomic_t cpu_count;
>> +};
>> +
>> +static int do_text_poke(void *data)
>> +{
>> + int ret = 0;
>> + struct text_poke_args *patch = data;
>> +
>> + if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
>> + ret = patch_text_nosync(patch->addr, patch->insns, patch->len);
>> + atomic_inc(&patch->cpu_count);
>> + } else {
>> + while (atomic_read(&patch->cpu_count) <= num_online_cpus())
>> + cpu_relax();
>> + smp_mb();
>> + }
>> +
>> + return ret;
>> +}
>> +
>> +static int bpf_text_poke_stop_machine(void *addr, const void *insns, size_t len)
>> +{
>> + struct text_poke_args patch = {
>> + .addr = addr,
>> + .insns = insns,
>> + .len = len,
>> + .cpu_count = ATOMIC_INIT(0),
>> + };
>> +
>> + return stop_machine(do_text_poke, &patch, cpu_online_mask);
>> +}
>> +
>> +static int gen_call_or_nops(void *target, void *ip, u32 *insns)
>> +{
>> + int i, ret;
>> + s64 rvoff;
>> + struct rv_jit_context ctx;
>> +
>> + ctx.ninsns = 0;
>> + ctx.insns = (u16 *)insns;
>> +
>> + if (!target) {
>> + for (i = 0; i < 4; i++)
>> + emit(rv_nop(), &ctx);
>> + return 0;
>> + }
>> +
>> + rvoff = (s64)(target - ip);
>> + emit(rv_sd(RV_REG_SP, -8, RV_REG_RA), &ctx);
>> + ret = emit_jump_and_link(RV_REG_RA, rvoff, false, &ctx);
>> + if (ret)
>> + return ret;
>> + emit(rv_ld(RV_REG_RA, -8, RV_REG_SP), &ctx);
>> +
>> + return 0;
>> +
>> +}
>> +
>> +static int bpf_text_poke_call(void *ip, void *old_addr, void *new_addr)
>> +{
>> + int ret;
>> + u32 old_insns[4], new_insns[4];
>> +
>> + ret = gen_call_or_nops(old_addr, ip + 4, old_insns);
>> + if (ret)
>> + return ret;
>> +
>> + ret = gen_call_or_nops(new_addr, ip + 4, new_insns);
>> + if (ret)
>> + return ret;
>> +
>> + mutex_lock(&text_mutex);
>> + if (memcmp(ip, old_insns, sizeof(old_insns))) {
>> + ret = -EFAULT;
>> + goto out;
>> + }
>> +
>> + if (memcmp(ip, new_insns, sizeof(new_insns)))
>> + ret = bpf_text_poke_stop_machine(ip, new_insns,
>> sizeof(new_insns));
>
> I'd rather see that you added a patch_text variant to
> arch/riscv/kernel/patch.c (something like your
> bpf_text_poke_stop_machine()), and use that here. Might be other users
> of that as well -- Andy's ftrace patch maybe? :-)
>
Good idea.
>> +out:
>> + mutex_unlock(&text_mutex);
>> + return ret;
>> +}
>> +
>> +static int bpf_text_poke_jump(void *ip, void *old_addr, void *new_addr)
>> +{
>> + int ret;
>> + u32 old_insn, new_insn;
>> +
>> + old_insn = old_addr ? rv_jal(RV_REG_ZERO, (s64)(old_addr - ip) >> 1) : rv_nop();
>> + new_insn = new_addr ? rv_jal(RV_REG_ZERO, (s64)(new_addr - ip) >> 1) : rv_nop();
>> +
>> + mutex_lock(&text_mutex);
>> + if (memcmp(ip, &old_insn, sizeof(old_insn))) {
>> + ret = -EFAULT;
>> + goto out;
>> + }
>> +
>> + if (memcmp(ip, &new_insn, sizeof(new_insn)))
>> + ret = patch_text_nosync(ip, &new_insn, sizeof(new_insn));
>> +out:
>> + mutex_unlock(&text_mutex);
>> + return ret;
>> +}
>> +
>> +int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type poke_type,
>> + void *old_addr, void *new_addr)
>
> AFAIU there's nothing in the bpf_arch_text_poke() API that say that
> BPF_MOD_JUMP is jumps within the trampoline. That is one usage, but not
> the only one. In general, the jal might not have enough reach.
>
> I believe that this needs to be an auipc/jalr pair similar to
> BPF_MOD_CALL (w/o linked register).
>
The initial idea was that currently BPF_MOD_JUMP only serves for
bpf_tramp_image_put, and jal, which range is +/- 1MB, is sufficient for
the distance between im->ip_after_call and im->ip_epilogue, and try to
not use not-atomic auipc/jalr pair. But take deep consideration, this
might be extended to other uses, such as tailcall optimization. So agree
with your suggestion.
>
> And again, thanks for working on the RV trampoline!
> Björn