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Message-ID: <d5e21238-89f4-444e-9c35-f4a28e01052e@ghiti.fr>
Date: Mon, 5 Feb 2024 07:22:04 +0100
From: Alexandre Ghiti <alex@...ti.fr>
To: Anup Patel <apatel@...tanamicro.com>, Palmer Dabbelt
<palmer@...belt.com>, Paul Walmsley <paul.walmsley@...ive.com>
Cc: Anup Patel <anup@...infault.org>, linux-kernel@...r.kernel.org,
Björn Töpel <bjorn@...nel.org>,
Atish Patra <atishp@...shpatra.org>, linux-riscv@...ts.infradead.org,
Andrew Jones <ajones@...tanamicro.com>
Subject: Re: [PATCH] RISC-V: Don't use IPIs in flush_icache_all() when
patching text
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@...nel.org>
> Closes: https://gist.github.com/bjoto/04a580568378f3b5483af07cd9d22501
> Signed-off-by: Anup Patel <apatel@...tanamicro.com>
> ---
> 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?
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);
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