Unverified Commit a638b046 authored by Sergey Matyukevich's avatar Sergey Matyukevich Committed by Palmer Dabbelt
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riscv: prevent pt_regs corruption for secondary idle threads 



Top of the kernel thread stack should be reserved for pt_regs. However
this is not the case for the idle threads of the secondary boot harts.
Their stacks overlap with their pt_regs, so both may get corrupted.

Similar issue has been fixed for the primary hart, see c7cdd96e
("riscv: prevent stack corruption by reserving task_pt_regs(p) early").
However that fix was not propagated to the secondary harts. The problem
has been noticed in some CPU hotplug tests with V enabled. The function
smp_callin stored several registers on stack, corrupting top of pt_regs
structure including status field. As a result, kernel attempted to save
or restore inexistent V context.

Fixes: 9a2451f1 ("RISC-V: Avoid using per cpu array for ordered booting")
Fixes: 2875fe05 ("RISC-V: Add cpu_ops and modify default booting method")
Signed-off-by: default avatarSergey Matyukevich <sergey.matyukevich@syntacore.com>
Reviewed-by: default avatarAlexandre Ghiti <alexghiti@rivosinc.com>
Link: https://lore.kernel.org/r/20240523084327.2013211-1-geomatsi@gmail.com


Signed-off-by: default avatarPalmer Dabbelt <palmer@rivosinc.com>
parent 1613e604

arch/riscv/kernel/cpu_ops_sbi.c

+1 −1
Original line number Diff line number Diff line
@@ -72,7 +72,7 @@ static int sbi_cpu_start(unsigned int cpuid, struct task_struct *tidle) 
	/* Make sure tidle is updated */

	smp_mb();

	bdata->task_ptr = tidle;

	bdata->stack_ptr = task_stack_page(tidle) + THREAD_SIZE;

	bdata->stack_ptr = task_pt_regs(tidle);

	/* Make sure boot data is updated */

	smp_mb();

	hsm_data = __pa(bdata);

arch/riscv/kernel/cpu_ops_spinwait.c

+1 −2
Original line number Diff line number Diff line
@@ -34,8 +34,7 @@ static void cpu_update_secondary_bootdata(unsigned int cpuid, 


	/* Make sure tidle is updated */

	smp_mb();

	WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid],

		   task_stack_page(tidle) + THREAD_SIZE);

	WRITE_ONCE(__cpu_spinwait_stack_pointer[hartid], task_pt_regs(tidle));

	WRITE_ONCE(__cpu_spinwait_task_pointer[hartid], tidle);

}