linux-kernel - [PATCH] x86/srat: Conditional apic_id vs MAX_LOCAL

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Message-ID: <E053FB6951F019A2+20250228051847.50002-1-wangyuli@uniontech.com>
Date: Fri, 28 Feb 2025 13:18:47 +0800
From: WangYuli <wangyuli@...ontech.com>
To: dave.hansen@...ux.intel.com,
	luto@...nel.org,
	peterz@...radead.org,
	tglx@...utronix.de,
	mingo@...hat.com,
	bp@...en8.de,
	x86@...nel.org,
	hpa@...or.com
Cc: linux-kernel@...r.kernel.org,
	zhanjun@...ontech.com,
	niecheng1@...ontech.com,
	chenlinxuan@...ontech.com,
	WangYuli <wangyuli@...ontech.com>,
	Huacai Chen <chenhuacai@...ngson.cn>,
	Wentao Guan <guanwentao@...ontech.com>
Subject: [PATCH] x86/srat: Conditional apic_id vs MAX_LOCAL_APIC comparison

The apic_id employed within the acpi_numa_processor_affinity_init()
function is derived from the acpi_srat_cpu_affinity structure defined
in acpi/actbl3.h.

When CONFIG_X86_X2APIC is not enabled, its maximum value is limited
to 255. It is only capable of exceeding 256 and 32768 —  which
corresponds to the definition of MAX_LOCAL_APIC — when CONFIG_X86_X2APIC
is activated.

Consequently, with CONFIG_X86_X2APIC disabled, this code segment will
elicit the compiler's "-Wtautological-constant-out-of-range-compare"
warning, as a variable capped at 255 can never satisfy a condition
requiring it to be greater than or equal to 256 or 32768.

Compiling the kernel with the W=1e flag will, in this scenario, lead
to compilation failure.

Suggested-by: Huacai Chen <chenhuacai@...ngson.cn>
Co-developed-by: Wentao Guan <guanwentao@...ontech.com>
Signed-off-by: Wentao Guan <guanwentao@...ontech.com>
Signed-off-by: WangYuli <wangyuli@...ontech.com>
---
 arch/x86/mm/srat.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/mm/srat.c b/arch/x86/mm/srat.c
index 6f8e0f21c710..93e5bcc58ead 100644
--- a/arch/x86/mm/srat.c
+++ b/arch/x86/mm/srat.c
@@ -90,10 +90,12 @@ acpi_numa_processor_affinity_init(struct acpi_srat_cpu_affinity *pa)
 	else
 		apic_id = pa->apic_id;

+#ifdef CONFIG_X86_X2APIC
 	if (apic_id >= MAX_LOCAL_APIC) {
 		printk(KERN_INFO "SRAT: PXM %u -> APIC 0x%02x -> Node %u skipped apicid that is too big\n", pxm, apic_id, node);
 		return;
 	}
+#endif /* CONFIG_X86_X2APIC */

 	set_apicid_to_node(apic_id, node);
 	node_set(node, numa_nodes_parsed);
-- 
2.47.2