Commit 79b92ab2 authored Dec 13, 2023 by Yury Norov Committed by Lu Jialin Dec 13, 2023

powerpc/64: don't refer nr_cpu_ids in asm code when it's undefined

mainline inclusion
from mainline-v6.1-rc1
commit 546a073d
category: cleanup
bugzilla: https://gitee.com/openeuler/kernel/issues/I8KQBZ
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=546a073d628111e3338af689938407e77d5dc38f



--------------------------------

generic_secondary_common_init() calls LOAD_REG_ADDR(r7, nr_cpu_ids)
conditionally on CONFIG_SMP. However, if 'NR_CPUS == 1', kernel doesn't
use the nr_cpu_ids, and in C code, it's just:
  #if NR_CPUS == 1
  #define nr_cpu_ids
  ...

This series makes declaration of nr_cpu_ids conditional on NR_CPUS == 1,
and that reveals the issue, because compiler can't link the
LOAD_REG_ADDR(r7, nr_cpu_ids) against nonexisting symbol.

Current code looks unsafe for those who build kernel with CONFIG_SMP=y and
NR_CPUS == 1. This is weird configuration, but not disallowed.

Fix the linker error by replacing LOAD_REG_ADDR() with LOAD_REG_IMMEDIATE()
conditionally on NR_CPUS == 1.

As the following patch adds CONFIG_FORCE_NR_CPUS option that has the
similar effect on nr_cpu_ids, make the generic_secondary_common_init()
conditional on it too.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Signed-off-by: Zheng Zucheng <zhengzucheng@huawei.com>

parent 67d0d7fe

arch/powerpc/kernel/head_64.S

+4 −0

Original line number	Diff line number	Diff line
		@@ -398,8 +398,12 @@ generic_secondary_common_init:
		#else
		LOAD_REG_ADDR(r8, paca_ptrs) /* Load paca_ptrs pointe */
		ld r8,0(r8) /* Get base vaddr of array */
		#if (NR_CPUS == 1) \|\| defined(CONFIG_FORCE_NR_CPUS)
		LOAD_REG_IMMEDIATE(r7, NR_CPUS)
		#else
		LOAD_REG_ADDR(r7, nr_cpu_ids) /* Load nr_cpu_ids address */
		lwz r7,0(r7) /* also the max paca allocated */
		#endif
		li r5,0 /* logical cpu id */
		1:
		sldi r9,r5,3 /* get paca_ptrs[] index from cpu id */