[PATCH 2/2] riscv: Disable preemption when using patch_map()

[Alexandre Ghiti]

patch_map() uses fixmap mappings to circumvent the non-writability of
the kernel text mapping.

The __set_fixmap() function only flushes the current cpu tlb, it does
not emit an IPI so we must make sure that while we use a fixmap mapping,
the current task is not migrated on another cpu which could miss the
newly introduced fixmap mapping.

So in order to avoid any task migration, disable the preemption.

Reported-by: Andrea Parri <andrea at rivosinc.com>
Closes: https://lore.kernel.org/all/ZcS+GAaM25LXsBOl@andrea/
Reported-by: Andy Chiu <andy.chiu at sifive.com>
Closes: https://lore.kernel.org/linux-riscv/CABgGipUMz3Sffu-CkmeUB1dKVwVQ73+7=sgC45-m0AE9RCjOZg@mail.gmail.com/
Fixes: cad539baa48f ("riscv: implement a memset like function for text")
Fixes: 0ff7c3b33127 ("riscv: Use text_mutex instead of patch_lock")
Co-developed-by: Andy Chiu <andy.chiu at sifive.com>
Signed-off-by: Andy Chiu <andy.chiu at sifive.com>
Signed-off-by: Alexandre Ghiti <alexghiti at rivosinc.com>
---
 arch/riscv/kernel/patch.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/riscv/kernel/patch.c b/arch/riscv/kernel/patch.c
index 37e87fdcf6a0..30e12b310cab 100644
--- a/arch/riscv/kernel/patch.c
+++ b/arch/riscv/kernel/patch.c
@@ -80,6 +80,8 @@ static int __patch_insn_set(void *addr, u8 c, size_t len)
 	 */
 	lockdep_assert_held(&text_mutex);
 
+	preempt_disable();
+
 	if (across_pages)
 		patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);
 
@@ -92,6 +94,8 @@ static int __patch_insn_set(void *addr, u8 c, size_t len)
 	if (across_pages)
 		patch_unmap(FIX_TEXT_POKE1);
 
+	preempt_enable();
+
 	return 0;
 }
 NOKPROBE_SYMBOL(__patch_insn_set);
@@ -122,6 +126,8 @@ static int __patch_insn_write(void *addr, const void *insn, size_t len)
 	if (!riscv_patch_in_stop_machine)
 		lockdep_assert_held(&text_mutex);
 
+	preempt_disable();
+
 	if (across_pages)
 		patch_map(addr + PAGE_SIZE, FIX_TEXT_POKE1);
 
@@ -134,6 +140,8 @@ static int __patch_insn_write(void *addr, const void *insn, size_t len)
 	if (across_pages)
 		patch_unmap(FIX_TEXT_POKE1);
 
+	preempt_enable();
+
 	return ret;
 }
 NOKPROBE_SYMBOL(__patch_insn_write);
-- 
2.39.2