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Subject[PATCH] RISC-V: insn: Use a raw spinlock to protect TEXT_POKE*
Date
From
From: Palmer Dabbelt <palmerdabbelt@google.com>

We currently use text_mutex to protect the fixmap sections from
concurrent callers. This is convienent for kprobes as the generic code
already holds text_mutex, but ftrace doesn't which triggers a lockdep
assertion. We could take text_mutex for ftrace, but the jump label
implementation (which is currently taking text_mutex) isn't explicitly
listed as being sleepable and it's called from enough places it seems
safer to just avoid sleeping.

arm64 and parisc, the other two TEXT_POKE-style patching
implemnetations, already use raw spinlocks. abffa6f3b157 ("arm64:
convert patch_lock to raw lock") lays out the case for a raw spinlock as
opposed to a regular spinlock, and while I don't know of anyone using rt
on RISC-V I'm sure it'll eventually show up and I don't see any reason
to wait.

Fixes: ebc00dde8a97 ("riscv: Add jump-label implementation")
Reported-by: Changbin Du <changbin.du@gmail.com>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
---
arch/riscv/include/asm/fixmap.h | 3 +++
arch/riscv/kernel/jump_label.c | 2 --
arch/riscv/kernel/patch.c | 13 +++++++++----
3 files changed, 12 insertions(+), 6 deletions(-)

diff --git a/arch/riscv/include/asm/fixmap.h b/arch/riscv/include/asm/fixmap.h
index 54cbf07fb4e9..d1c0a1f123cf 100644
--- a/arch/riscv/include/asm/fixmap.h
+++ b/arch/riscv/include/asm/fixmap.h
@@ -24,8 +24,11 @@ enum fixed_addresses {
FIX_HOLE,
FIX_PTE,
FIX_PMD,
+
+ /* Only used in kernel/insn.c */
FIX_TEXT_POKE1,
FIX_TEXT_POKE0,
+
FIX_EARLYCON_MEM_BASE,

__end_of_permanent_fixed_addresses,
diff --git a/arch/riscv/kernel/jump_label.c b/arch/riscv/kernel/jump_label.c
index 20e09056d141..45bb32f91b5c 100644
--- a/arch/riscv/kernel/jump_label.c
+++ b/arch/riscv/kernel/jump_label.c
@@ -35,9 +35,7 @@ void arch_jump_label_transform(struct jump_entry *entry,
insn = RISCV_INSN_NOP;
}

- mutex_lock(&text_mutex);
patch_text_nosync(addr, &insn, sizeof(insn));
- mutex_unlock(&text_mutex);
}

void arch_jump_label_transform_static(struct jump_entry *entry,
diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 0b552873a577..dfa7ee8eb63f 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -19,6 +19,8 @@ struct patch_insn {
atomic_t cpu_count;
};

+static DEFINE_RAW_SPINLOCK(patch_lock);
+
#ifdef CONFIG_MMU
/*
* The fix_to_virt(, idx) needs a const value (not a dynamic variable of
@@ -54,13 +56,14 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
void *waddr = addr;
bool across_pages = (((uintptr_t) addr & ~PAGE_MASK) + len) > PAGE_SIZE;
int ret;
+ unsigned long flags = 0;

/*
- * Before reaching here, it was expected to lock the text_mutex
- * already, so we don't need to give another lock here and could
- * ensure that it was safe between each cores.
+ * FIX_TEXT_POKE{0,1} are only used for text patching, but we must
+ * ensure that concurrent callers do not re-map these before we're done
+ * with them.
*/
- lockdep_assert_held(&text_mutex);
+ raw_spin_lock_irqsave(&patch_lock, flags);

if (across_pages)
patch_map(addr + len, FIX_TEXT_POKE1);
@@ -74,6 +77,8 @@ static int patch_insn_write(void *addr, const void *insn, size_t len)
if (across_pages)
patch_unmap(FIX_TEXT_POKE1);

+ raw_spin_unlock_irqrestore(&patch_lock, flags);
+
return ret;
}
NOKPROBE_SYMBOL(patch_insn_write);
--
2.31.1.498.g6c1eba8ee3d-goog
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