[PATCH v1] RISC-V: take text_mutex during alternative patching

[Conor Dooley]

From: Conor Dooley <conor.dooley at microchip.com>

Guenter reported a splat during boot, that Samuel pointed out was the
lockdep assertion failing in patch_insn_write():

WARNING: CPU: 0 PID: 0 at arch/riscv/kernel/patch.c:63 patch_insn_write+0x222/0x2f6
epc : patch_insn_write+0x222/0x2f6
 ra : patch_insn_write+0x21e/0x2f6
epc : ffffffff800068c6 ra : ffffffff800068c2 sp : ffffffff81803df0
 gp : ffffffff81a1ab78 tp : ffffffff81814f80 t0 : ffffffffffffe000
 t1 : 0000000000000001 t2 : 4c45203a76637369 s0 : ffffffff81803e40
 s1 : 0000000000000004 a0 : 0000000000000000 a1 : ffffffffffffffff
 a2 : 0000000000000004 a3 : 0000000000000000 a4 : 0000000000000001
 a5 : 0000000000000000 a6 : 0000000000000000 a7 : 0000000052464e43
 s2 : ffffffff80b4889c s3 : 000000000000082c s4 : ffffffff80b48828
 s5 : 0000000000000828 s6 : ffffffff8131a0a0 s7 : 0000000000000fff
 s8 : 0000000008000200 s9 : ffffffff8131a520 s10: 0000000000000018
 s11: 000000000000000b t3 : 0000000000000001 t4 : 000000000000000d
 t5 : ffffffffd8180000 t6 : ffffffff81803bc8
status: 0000000200000100 badaddr: 0000000000000000 cause: 0000000000000003
[<ffffffff800068c6>] patch_insn_write+0x222/0x2f6
[<ffffffff80006a36>] patch_text_nosync+0xc/0x2a
[<ffffffff80003b86>] riscv_cpufeature_patch_func+0x52/0x98
[<ffffffff80003348>] _apply_alternatives+0x46/0x86
[<ffffffff80c02d36>] apply_boot_alternatives+0x3c/0xfa
[<ffffffff80c03ad8>] setup_arch+0x584/0x5b8
[<ffffffff80c0075a>] start_kernel+0xa2/0x8f8

This issue was exposed by 702e64550b12 ("riscv: fpu: switch has_fpu() to
riscv_has_extension_likely()"), as it is the patching in has_fpu() that
triggers the splats in Guenter's report.

Take the text_mutex before doing any code patching to satisfy lockdep.

Fixes: ff689fd21cb1 ("riscv: add RISC-V Svpbmt extension support")
Fixes: a35707c3d850 ("riscv: add memory-type errata for T-Head")
Fixes: 1a0e5dbd3723 ("riscv: sifive: Add SiFive alternative ports")
Reported-by: Guenter Roeck <linux at roeck-us.net>
Link: https://lore.kernel.org/all/20230212154333.GA3760469@roeck-us.net/
Signed-off-by: Conor Dooley <conor.dooley at microchip.com>
---
Applies on top of Samuel's critical fixes in his "Fix alternatives
issues on for-next":
https://lore.kernel.org/all/20230212021534.59121-1-samuel@sholland.org/
---
 arch/riscv/errata/sifive/errata.c | 3 +++
 arch/riscv/errata/thead/errata.c  | 8 ++++++--
 arch/riscv/kernel/cpufeature.c    | 4 ++++
 3 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/errata/sifive/errata.c b/arch/riscv/errata/sifive/errata.c
index ef9a4eec0dba..da55cb247e89 100644
--- a/arch/riscv/errata/sifive/errata.c
+++ b/arch/riscv/errata/sifive/errata.c
@@ -4,6 +4,7 @@
  */
 
 #include <linux/kernel.h>
+#include <linux/memory.h>
 #include <linux/module.h>
 #include <linux/string.h>
 #include <linux/bug.h>
@@ -107,8 +108,10 @@ void __init_or_module sifive_errata_patch_func(struct alt_entry *begin,
 
 		tmp = (1U << alt->errata_id);
 		if (cpu_req_errata & tmp) {
+			mutex_lock(&text_mutex);
 			patch_text_nosync(ALT_OLD_PTR(alt), ALT_ALT_PTR(alt),
 					  alt->alt_len);
+			mutex_lock(&text_mutex);
 			cpu_apply_errata |= tmp;
 		}
 	}
diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
index 1dd90a5f86f0..3b96a06d3c54 100644
--- a/arch/riscv/errata/thead/errata.c
+++ b/arch/riscv/errata/thead/errata.c
@@ -5,6 +5,7 @@
 
 #include <linux/bug.h>
 #include <linux/kernel.h>
+#include <linux/memory.h>
 #include <linux/module.h>
 #include <linux/string.h>
 #include <linux/uaccess.h>
@@ -101,10 +102,13 @@ void __init_or_module thead_errata_patch_func(struct alt_entry *begin, struct al
 			altptr = ALT_ALT_PTR(alt);
 
 			/* On vm-alternatives, the mmu isn't running yet */
-			if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
+			if (stage == RISCV_ALTERNATIVES_EARLY_BOOT) {
 				memcpy(oldptr, altptr, alt->alt_len);
-			else
+			} else {
+				mutex_lock(&text_mutex);
 				patch_text_nosync(oldptr, altptr, alt->alt_len);
+				mutex_unlock(&text_mutex);
+			}
 		}
 	}
 
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 21fb567e1b22..59d58ee0f68d 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -10,6 +10,7 @@
 #include <linux/ctype.h>
 #include <linux/libfdt.h>
 #include <linux/log2.h>
+#include <linux/memory.h>
 #include <linux/module.h>
 #include <linux/of.h>
 #include <asm/alternative.h>
@@ -292,8 +293,11 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin,
 
 		oldptr = ALT_OLD_PTR(alt);
 		altptr = ALT_ALT_PTR(alt);
+
+		mutex_lock(&text_mutex);
 		patch_text_nosync(oldptr, altptr, alt->alt_len);
 		riscv_alternative_fix_offsets(oldptr, alt->alt_len, oldptr - altptr);
+		mutex_unlock(&text_mutex);
 	}
 }
 #endif
-- 
2.39.1