Re: [PATCH 2/2] riscv: Fix text patching when IPI are used

From: Alexandre Ghiti
Date: Wed Feb 28 2024 - 14:02:57 EST

On Wed, Feb 28, 2024 at 7:21 PM Samuel Holland
<samuel.holland@xxxxxxxxxx> wrote:
>
> Hi Alex,
>
> On 2024-02-28 11:51 AM, Alexandre Ghiti wrote:
> > For now, we use stop_machine() to patch the text and when we use IPIs for
> > remote icache flushes (which is emitted in patch_text_nosync()), the system
> > hangs.
> >
> > So instead, make sure every cpu executes the stop_machine() patching
> > function and emit a local icache flush there.
> >
> > Co-developed-by: Björn Töpel <bjorn@xxxxxxxxxxxx>
> > Signed-off-by: Björn Töpel <bjorn@xxxxxxxxxxxx>
> > Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> > ---
> > arch/riscv/include/asm/patch.h | 1 +
> > arch/riscv/kernel/ftrace.c | 42 ++++++++++++++++++++++++++++++----
> > arch/riscv/kernel/patch.c | 18 +++++++++------
> > 3 files changed, 50 insertions(+), 11 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/patch.h b/arch/riscv/include/asm/patch.h
> > index e88b52d39eac..9f5d6e14c405 100644
> > --- a/arch/riscv/include/asm/patch.h
> > +++ b/arch/riscv/include/asm/patch.h
> > @@ -6,6 +6,7 @@
> > #ifndef _ASM_RISCV_PATCH_H
> > #define _ASM_RISCV_PATCH_H
> >
> > +int patch_insn_write(void *addr, const void *insn, size_t len);
> > int patch_text_nosync(void *addr, const void *insns, size_t len);
> > int patch_text_set_nosync(void *addr, u8 c, size_t len);
> > int patch_text(void *addr, u32 *insns, int ninsns);
> > diff --git a/arch/riscv/kernel/ftrace.c b/arch/riscv/kernel/ftrace.c
> > index f5aa24d9e1c1..5654966c4e7d 100644
> > --- a/arch/riscv/kernel/ftrace.c
> > +++ b/arch/riscv/kernel/ftrace.c
> > @@ -8,6 +8,7 @@
> > #include <linux/ftrace.h>
> > #include <linux/uaccess.h>
> > #include <linux/memory.h>
> > +#include <linux/stop_machine.h>
> > #include <asm/cacheflush.h>
> > #include <asm/patch.h>
> >
> > @@ -75,8 +76,7 @@ static int __ftrace_modify_call(unsigned long hook_pos, unsigned long target,
> > make_call_t0(hook_pos, target, call);
> >
> > /* Replace the auipc-jalr pair at once. Return -EPERM on write error. */
> > - if (patch_text_nosync
> > - ((void *)hook_pos, enable ? call : nops, MCOUNT_INSN_SIZE))
> > + if (patch_insn_write((void *)hook_pos, enable ? call : nops, MCOUNT_INSN_SIZE))
> > return -EPERM;
> >
> > return 0;
> > @@ -88,7 +88,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> >
> > make_call_t0(rec->ip, addr, call);
> >
> > - if (patch_text_nosync((void *)rec->ip, call, MCOUNT_INSN_SIZE))
> > + if (patch_insn_write((void *)rec->ip, call, MCOUNT_INSN_SIZE))
> > return -EPERM;
> >
> > return 0;
> > @@ -99,7 +99,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
> > {
> > unsigned int nops[2] = {NOP4, NOP4};
> >
> > - if (patch_text_nosync((void *)rec->ip, nops, MCOUNT_INSN_SIZE))
> > + if (patch_insn_write((void *)rec->ip, nops, MCOUNT_INSN_SIZE))
> > return -EPERM;
> >
> > return 0;
> > @@ -134,6 +134,40 @@ int ftrace_update_ftrace_func(ftrace_func_t func)
> >
> > return ret;
> > }
> > +
> > +struct ftrace_modify_param {
> > + int command;
> > + atomic_t cpu_count;
> > +};
> > +
> > +static int __ftrace_modify_code(void *data)
> > +{
> > + struct ftrace_modify_param *param = data;
> > +
> > + if (atomic_inc_return(&param->cpu_count) == num_online_cpus()) {
> > + ftrace_modify_all_code(param->command);
> > + /*
> > + * Make sure the patching store is effective *before* we
> > + * increment the counter which releases all waiting cpus
> > + * by using the release version of atomic increment.
> > + */
> > + atomic_inc_return_release(&param->cpu_count);
> > + } else {
> > + while (atomic_read(&param->cpu_count) <= num_online_cpus())
> > + cpu_relax();
> > + }
> > +
> > + local_flush_icache_all();
> > +
> > + return 0;
> > +}
> > +
> > +void arch_ftrace_update_code(int command)
> > +{
> > + struct ftrace_modify_param param = { command, ATOMIC_INIT(0) };
> > +
> > + stop_machine(__ftrace_modify_code, &param, cpu_online_mask);
> > +}
> > #endif
> >
> > #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
> > diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> > index 0b5c16dfe3f4..82d8508c765b 100644
> > --- a/arch/riscv/kernel/patch.c
> > +++ b/arch/riscv/kernel/patch.c
> > @@ -188,7 +188,7 @@ int patch_text_set_nosync(void *addr, u8 c, size_t len)
> > }
> > NOKPROBE_SYMBOL(patch_text_set_nosync);
> >
> > -static int patch_insn_write(void *addr, const void *insn, size_t len)
> > +int patch_insn_write(void *addr, const void *insn, size_t len)
> > {
> > size_t patched = 0;
> > size_t size;
> > @@ -211,11 +211,9 @@ NOKPROBE_SYMBOL(patch_insn_write);
> >
> > int patch_text_nosync(void *addr, const void *insns, size_t len)
> > {
> > - u32 *tp = addr;
> > int ret;
> >
> > - ret = patch_insn_write(tp, insns, len);
> > -
> > + ret = patch_insn_write(addr, insns, len);
> > if (!ret)
> > flush_icache_range((uintptr_t) tp, (uintptr_t) tp + len);
>
> This only happens to compile because flush_icache_range() is a macro that
> ignores its parameters. You could replace tp with addr in this line as well, but
> that seems like more of a cosmetic change and should be a separate patch (like
> in [1] which covers both related functions) if you respin this.

I'll respin a new version and won't touch the extra variables since
you did. Your patchset is getting closer and closer in my todo list :)

Thanks,

Alex

>
> Regards,
> Samuel
>
> [1]:
> https://lore.kernel.org/linux-riscv/20240212025529.1971876-8-samuel.holland@xxxxxxxxxx/
>
> >
> > @@ -232,15 +230,21 @@ static int patch_text_cb(void *data)
> > if (atomic_inc_return(&patch->cpu_count) == num_online_cpus()) {
> > for (i = 0; ret == 0 && i < patch->ninsns; i++) {
> > len = GET_INSN_LENGTH(patch->insns[i]);
> > - ret = patch_text_nosync(patch->addr + i * len,
> > - &patch->insns[i], len);
> > + ret = patch_insn_write(patch->addr + i * len, &patch->insns[i], len);
> > }
> > - atomic_inc(&patch->cpu_count);
> > + /*
> > + * Make sure the patching store is effective *before* we
> > + * increment the counter which releases all waiting cpus
> > + * by using the release version of atomic increment.
> > + */
> > + atomic_inc_return_release(&patch->cpu_count);
> > } else {
> > while (atomic_read(&patch->cpu_count) <= num_online_cpus())
> > cpu_relax();
> > }
> >
> > + local_flush_icache_all();
> > +
> > return ret;
> > }
> > NOKPROBE_SYMBOL(patch_text_cb);
>