linux-kernel - [PATCH v2] riscv: force __cpu_up_ variables to put in data section

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Message-Id: <20200504035448.13893-1-zong.li@sifive.com>
Date:   Mon,  4 May 2020 11:54:48 +0800
From:   Zong Li <zong.li@...ive.com>
To:     palmer@...belt.com, paul.walmsley@...ive.com,
        atishp@...shpatra.org, anup@...infault.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Zong Li <zong.li@...ive.com>,
        Greentime Hu <greentime.hu@...ive.com>
Subject: [PATCH v2] riscv: force __cpu_up_ variables to put in data section

Put __cpu_up_stack_pointer and __cpu_up_task_pointer in data section.
Currently, these two variables are put in bss section, there is a
potential risk that secondary harts get the uninitialized value before
main hart finishing the bss clearing. In this case, all secondary
harts would pass the waiting loop and enable the MMU before main hart
set up the page table.

This issue happened on random booting of multiple harts, which means
it will manifest for BBL and OpenSBI which older than v0.6. In OpenSBI
v0.7, it had included HSM extension, all the secondary harts are
waiting in firmware, so it could work fine without this change.

Changes in v2:
  - Add commit description about random booting.

Signed-off-by: Zong Li <zong.li@...ive.com>
Reviewed-by: Greentime Hu <greentime.hu@...ive.com>
---
 arch/riscv/kernel/cpu_ops.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/kernel/cpu_ops.c b/arch/riscv/kernel/cpu_ops.c
index c4c33bf02369..0ec22354018c 100644
--- a/arch/riscv/kernel/cpu_ops.c
+++ b/arch/riscv/kernel/cpu_ops.c
@@ -15,8 +15,8 @@

 const struct cpu_operations *cpu_ops[NR_CPUS] __ro_after_init;

-void *__cpu_up_stack_pointer[NR_CPUS];
-void *__cpu_up_task_pointer[NR_CPUS];
+void *__cpu_up_stack_pointer[NR_CPUS] __section(.data);
+void *__cpu_up_task_pointer[NR_CPUS] __section(.data);

 extern const struct cpu_operations cpu_ops_sbi;
 extern const struct cpu_operations cpu_ops_spinwait;
-- 
2.26.1