Re: [PATCH] RISC-V: Don't use IPIs in flush_icache_all() when patching text
From: Anup Patel
Date: Mon Feb 05 2024 - 04:56:23 EST
On Mon, Feb 5, 2024 at 11:52 AM Alexandre Ghiti <alex@xxxxxxxx> wrote:
>
> Hi Anup,
>
> On 05/02/2024 05:29, Anup Patel wrote:
> > If some of the HARTs are parked by stop machine then IPI-based
> > flushing in flush_icache_all() will hang. This hang is observed
> > when text patching is invoked by various debug and BPF features.
> >
> > To avoid this hang, we force use of SBI-based icache flushing
> > when patching text.
> >
> > Fixes: 627922843235 ("RISC-V: Use IPIs for remote icache flush when possible")
> > Reported-by: Bjorn Topel <bjorn@xxxxxxxxxx>
> > Closes: https://gist.github.com/bjoto/04a580568378f3b5483af07cd9d22501
> > Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> > ---
> > arch/riscv/include/asm/cacheflush.h | 7 ++++---
> > arch/riscv/kernel/hibernate.c | 2 +-
> > arch/riscv/kernel/patch.c | 4 ++--
> > arch/riscv/mm/cacheflush.c | 7 ++++---
> > 4 files changed, 11 insertions(+), 9 deletions(-)
> >
> > diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h
> > index a129dac4521d..561e079f34af 100644
> > --- a/arch/riscv/include/asm/cacheflush.h
> > +++ b/arch/riscv/include/asm/cacheflush.h
> > @@ -32,7 +32,8 @@ static inline void flush_dcache_page(struct page *page)
> > * RISC-V doesn't have an instruction to flush parts of the instruction cache,
> > * so instead we just flush the whole thing.
> > */
> > -#define flush_icache_range(start, end) flush_icache_all()
> > +#define flush_icache_range(start, end) flush_icache_all(true)
> > +#define flush_icache_patch_range(start, end) flush_icache_all(false)
> > #define flush_icache_user_page(vma, pg, addr, len) \
> > flush_icache_mm(vma->vm_mm, 0)
> >
> > @@ -43,12 +44,12 @@ static inline void flush_dcache_page(struct page *page)
> >
> > #ifndef CONFIG_SMP
> >
> > -#define flush_icache_all() local_flush_icache_all()
> > +#define flush_icache_all(want_ipi) local_flush_icache_all()
> > #define flush_icache_mm(mm, local) flush_icache_all()
> >
> > #else /* CONFIG_SMP */
> >
> > -void flush_icache_all(void);
> > +void flush_icache_all(bool want_ipi);
> > void flush_icache_mm(struct mm_struct *mm, bool local);
> >
> > #endif /* CONFIG_SMP */
> > diff --git a/arch/riscv/kernel/hibernate.c b/arch/riscv/kernel/hibernate.c
> > index 671b686c0158..388f10e187ba 100644
> > --- a/arch/riscv/kernel/hibernate.c
> > +++ b/arch/riscv/kernel/hibernate.c
> > @@ -153,7 +153,7 @@ int swsusp_arch_suspend(void)
> > } else {
> > suspend_restore_csrs(hibernate_cpu_context);
> > flush_tlb_all();
> > - flush_icache_all();
> > + flush_icache_all(true);
> >
> > /*
> > * Tell the hibernation core that we've just restored the memory.
> > diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> > index 37e87fdcf6a0..721e144a7847 100644
> > --- a/arch/riscv/kernel/patch.c
> > +++ b/arch/riscv/kernel/patch.c
> > @@ -182,7 +182,7 @@ int patch_text_set_nosync(void *addr, u8 c, size_t len)
> > ret = patch_insn_set(tp, c, len);
> >
> > if (!ret)
> > - flush_icache_range((uintptr_t)tp, (uintptr_t)tp + len);
> > + flush_icache_patch_range((uintptr_t)tp, (uintptr_t)tp + len);
> >
> > return ret;
> > }
> > @@ -217,7 +217,7 @@ int patch_text_nosync(void *addr, const void *insns, size_t len)
> > ret = patch_insn_write(tp, insns, len);
> >
> > if (!ret)
> > - flush_icache_range((uintptr_t) tp, (uintptr_t) tp + len);
> > + flush_icache_patch_range((uintptr_t) tp, (uintptr_t) tp + len);
> >
> > return ret;
> > }
> > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> > index 55a34f2020a8..03cd3d4831ef 100644
> > --- a/arch/riscv/mm/cacheflush.c
> > +++ b/arch/riscv/mm/cacheflush.c
> > @@ -17,11 +17,12 @@ static void ipi_remote_fence_i(void *info)
> > return local_flush_icache_all();
> > }
> >
> > -void flush_icache_all(void)
> > +void flush_icache_all(bool want_ipi)
> > {
> > local_flush_icache_all();
> >
> > - if (IS_ENABLED(CONFIG_RISCV_SBI) && !riscv_use_ipi_for_rfence())
> > + if (IS_ENABLED(CONFIG_RISCV_SBI) &&
> > + (!want_ipi || !riscv_use_ipi_for_rfence()))
> > sbi_remote_fence_i(NULL);
> > else
> > on_each_cpu(ipi_remote_fence_i, NULL, 1);
> > @@ -87,7 +88,7 @@ void flush_icache_pte(pte_t pte)
> > struct folio *folio = page_folio(pte_page(pte));
> >
> > if (!test_bit(PG_dcache_clean, &folio->flags)) {
> > - flush_icache_all();
> > + flush_icache_all(true);
> > set_bit(PG_dcache_clean, &folio->flags);
> > }
> > }
>
>
> Since patch_text_cb() is run on all cpus, couldn't we completely avoid
> any remote icache flush by slightly changing patch_text_cb() instead as
> follows?
Unfortunately patch_text_cb() is not the only user of patch_text_nosync
since patch_text_nosync() and patch_text_set_nosync() are called directly
from other places as well.
We have to update all users of patch_text_nosync() and
patch_text_set_nosync() to move to local icache flushes which
is a much bigger change.
Regards,
Anup
>
> diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
> index 37e87fdcf6a0..075c376ed528 100644
> --- a/arch/riscv/kernel/patch.c
> +++ b/arch/riscv/kernel/patch.c
> @@ -232,8 +232,8 @@ 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((u32 *)(patch->addr + i *
> len),
> + &patch->insns[i], len);
> }
> atomic_inc(&patch->cpu_count);
> } else {
> @@ -242,6 +242,8 @@ static int patch_text_cb(void *data)
> smp_mb();
> }
>
> + local_flush_icache_all();
> +
> return ret;
> }
> NOKPROBE_SYMBOL(patch_text_cb);
>
>
>