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d="scan'208";a="312947855" Received: from unknown (HELO gm-smtp11.centrum.cz) ([46.255.227.75]) by antispam30.centrum.cz with ESMTP; 07 Apr 2025 15:25:07 +0200 Received: from localhost.localdomain (ip-213-220-240-96.bb.vodafone.cz [213.220.240.96]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by gm-smtp11.centrum.cz (Postfix) with ESMTPSA id F2BC0100AE2A3; Mon, 7 Apr 2025 15:25:06 +0200 (CEST) From: =?utf-8?q?Petr_Van=C4=9Bk?= To: Thomas Gleixner Cc: Andrew Cooper , arkamar@atlas.cz, Juergen Gross , linux-kernel@vger.kernel.org, stable@vger.kernel.org, x86@kernel.org, xen-devel@lists.xenproject.org, linux-acpi@vger.kernel.org Subject: [PATCH v2 1/1] x86/acpi: Don't limit CPUs to 1 for Xen PV guests due to disabled ACPI Date: Mon, 7 Apr 2025 15:24:27 +0200 Message-ID: <20250407132445.6732-2-arkamar@atlas.cz> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250407132445.6732-1-arkamar@atlas.cz> References: <87ecy5wqjm.ffs@tglx> <20250407132445.6732-1-arkamar@atlas.cz> Precedence: bulk X-Mailing-List: linux-acpi@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Xen disables ACPI for PV guests in DomU, which causes acpi_mps_check() to return 1 when CONFIG_X86_MPPARSE is not set. As a result, APIC is disabled and the guest is later limited to a single vCPU, despite being configured with more. This regression was introduced in version 6.9 in commit 7c0edad3643f ("x86/cpu/topology: Rework possible CPU management"), which added an early check that limits CPUs to 1 if apic_is_disabled. This patch updates acpi_mps_check() logic to return 0 early when running as a Xen PV guest in DomU, preventing APIC from being disabled in this specific case and restoring correct multi-vCPU behaviour. Fixes: 7c0edad3643f ("x86/cpu/topology: Rework possible CPU management") Cc: Thomas Gleixner Cc: x86@kernel.org Cc: xen-devel@lists.xenproject.org Cc: stable@vger.kernel.org # 6.9+ Signed-off-by: Petr Vaněk --- arch/x86/kernel/acpi/boot.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/arch/x86/kernel/acpi/boot.c b/arch/x86/kernel/acpi/boot.c index dae6a73be40e..9fa321a95eb3 100644 --- a/arch/x86/kernel/acpi/boot.c +++ b/arch/x86/kernel/acpi/boot.c @@ -23,6 +23,8 @@ #include #include +#include + #include #include #include @@ -1729,6 +1731,15 @@ int __init acpi_mps_check(void) { #if defined(CONFIG_X86_LOCAL_APIC) && !defined(CONFIG_X86_MPPARSE) /* mptable code is not built-in*/ + + /* + * Xen disables ACPI in PV DomU guests but it still emulates APIC and + * supports SMP. Returning early here ensures that APIC is not disabled + * unnecessarily and the guest is not limited to a single vCPU. + */ + if (xen_pv_domain() && !xen_initial_domain()) + return 0; + if (acpi_disabled || acpi_noirq) { pr_warn("MPS support code is not built-in, using acpi=off or acpi=noirq or pci=noacpi may have problem\n"); return 1;