linux-kernel - [PATCH] RISC-V: Check clint_time

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Date:   Sat, 26 Sep 2020 12:57:50 +0530
From:   Anup Patel <anup.patel@....com>
To:     Palmer Dabbelt <palmer@...belt.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Albert Ou <aou@...s.berkeley.edu>
Cc:     Atish Patra <atish.patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        Damien Le Moal <damien.lemoal@....com>,
        Anup Patel <anup@...infault.org>,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Anup Patel <anup.patel@....com>
Subject: [PATCH] RISC-V: Check clint_time_val before use

The NoMMU kernel is broken for QEMU virt machine from Linux-5.9-rc6
because the get_cycles() and friends are called very early from
rand_initialize() before CLINT driver is probed. To fix this, we
should check clint_time_val before use in get_cycles() and friends.

Fixes: d5be89a8d118 ("RISC-V: Resurrect the MMIO timer implementation
for M-mode systems")
Signed-off-by: Anup Patel <anup.patel@....com>
---
 arch/riscv/include/asm/timex.h | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/include/asm/timex.h b/arch/riscv/include/asm/timex.h
index 7f659dda0032..52b42bb1602c 100644
--- a/arch/riscv/include/asm/timex.h
+++ b/arch/riscv/include/asm/timex.h
@@ -17,18 +17,24 @@ typedef unsigned long cycles_t;
 #ifdef CONFIG_64BIT
 static inline cycles_t get_cycles(void)
 {
-	return readq_relaxed(clint_time_val);
+	if (clint_time_val)
+		return readq_relaxed(clint_time_val);
+	return 0;
 }
 #else /* !CONFIG_64BIT */
 static inline u32 get_cycles(void)
 {
-	return readl_relaxed(((u32 *)clint_time_val));
+	if (clint_time_val)
+		return readl_relaxed(((u32 *)clint_time_val));
+	return 0;
 }
 #define get_cycles get_cycles
 
 static inline u32 get_cycles_hi(void)
 {
-	return readl_relaxed(((u32 *)clint_time_val) + 1);
+	if (clint_time_val)
+		return readl_relaxed(((u32 *)clint_time_val) + 1);
+	return 0
 }
 #define get_cycles_hi get_cycles_hi
 #endif /* CONFIG_64BIT */
-- 
2.25.1