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From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Yury Norov <yury.norov@gmail.com>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Sasha Levin <sashal@kernel.org>,
	mpe@ellerman.id.au, christophe.leroy@csgroup.eu, aik@ozlabs.ru,
	amodra@au1.ibm.com, dja@axtens.net,
	linuxppc-dev@lists.ozlabs.org
Subject: [PATCH AUTOSEL 4.19 05/10] powerpc/64: don't refer nr_cpu_ids in asm code when it's undefined
Date: Mon, 17 Oct 2022 20:11:23 -0400	[thread overview]
Message-ID: <20221018001128.2732162-5-sashal@kernel.org> (raw)
In-Reply-To: <20221018001128.2732162-1-sashal@kernel.org>

From: Yury Norov <yury.norov@gmail.com>

[ Upstream commit 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: Sasha Levin <sashal@kernel.org>
---
 arch/powerpc/kernel/head_64.S | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 4f7b225d78cf..4215439a4663 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -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 */
-- 
2.35.1


WARNING: multiple messages have this Message-ID (diff)
From: Sasha Levin <sashal@kernel.org>
To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
Cc: Sasha Levin <sashal@kernel.org>,
	Stephen Rothwell <sfr@canb.auug.org.au>,
	Yury Norov <yury.norov@gmail.com>,
	aik@ozlabs.ru, amodra@au1.ibm.com, linuxppc-dev@lists.ozlabs.org,
	dja@axtens.net
Subject: [PATCH AUTOSEL 4.19 05/10] powerpc/64: don't refer nr_cpu_ids in asm code when it's undefined
Date: Mon, 17 Oct 2022 20:11:23 -0400	[thread overview]
Message-ID: <20221018001128.2732162-5-sashal@kernel.org> (raw)
In-Reply-To: <20221018001128.2732162-1-sashal@kernel.org>

From: Yury Norov <yury.norov@gmail.com>

[ Upstream commit 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: Sasha Levin <sashal@kernel.org>
---
 arch/powerpc/kernel/head_64.S | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/head_64.S b/arch/powerpc/kernel/head_64.S
index 4f7b225d78cf..4215439a4663 100644
--- a/arch/powerpc/kernel/head_64.S
+++ b/arch/powerpc/kernel/head_64.S
@@ -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 */
-- 
2.35.1


  parent reply	other threads:[~2022-10-18  0:17 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-18  0:11 [PATCH AUTOSEL 4.19 01/10] crypto: qcom-rng - Fix qcom_rng_of_match unused warning Sasha Levin
2022-10-18  0:11 ` [PATCH AUTOSEL 4.19 02/10] of/fdt: Don't calculate initrd size from DT if start > end Sasha Levin
2022-10-18  0:11 ` [PATCH AUTOSEL 4.19 03/10] objtool,x86: Teach decode about LOOP* instructions Sasha Levin
2022-10-18  0:11 ` [PATCH AUTOSEL 4.19 04/10] gfs2: Check sb_bsize_shift after reading superblock Sasha Levin
2022-10-18  0:11   ` [Cluster-devel] " Sasha Levin
2022-10-18  0:11 ` Sasha Levin [this message]
2022-10-18  0:11   ` [PATCH AUTOSEL 4.19 05/10] powerpc/64: don't refer nr_cpu_ids in asm code when it's undefined Sasha Levin
2022-10-18  0:11 ` [PATCH AUTOSEL 4.19 06/10] m68knommu: fix non-specific 68328 choice interrupt build failure Sasha Levin
2022-10-18  0:11 ` [PATCH AUTOSEL 4.19 07/10] m68knommu: fix non-mmu classic 68000 legacy timer tick selection Sasha Levin
2022-10-18  0:11 ` [PATCH AUTOSEL 4.19 08/10] 9p: trans_fd/p9_conn_cancel: drop client lock earlier Sasha Levin
2022-10-18  0:11 ` [PATCH AUTOSEL 4.19 09/10] 9p/trans_fd: always use O_NONBLOCK read/write Sasha Levin
2022-10-18  0:11 ` [PATCH AUTOSEL 4.19 10/10] virtio_pci: don't try to use intxif pin is zero Sasha Levin
2022-10-18  0:11   ` Sasha Levin

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