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d="scan'208";a="110176982" Received: from unknown (HELO gm-smtp10.centrum.cz) ([46.255.225.77]) by antispam35.centrum.cz with ESMTP; 05 Apr 2025 20:17:06 +0200 Received: from localhost.localdomain (nat-86.starnet.cz [178.255.168.86]) (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-smtp10.centrum.cz (Postfix) with ESMTPSA id 310E3809119F; Sat, 5 Apr 2025 20:17:06 +0200 (CEST) From: =?UTF-8?q?Petr=20Van=C4=9Bk?= To: linux-kernel@vger.kernel.org Cc: Thomas Gleixner , x86@kernel.org, xen-devel@lists.xenproject.org, =?UTF-8?q?Petr=20Van=C4=9Bk?= , stable@vger.kernel.org Subject: [PATCH 1/1] x86/cpu/topology: Don't limit CPUs to 1 for Xen PV guests due to disabled APIC Date: Sat, 5 Apr 2025 20:16:50 +0200 Message-ID: <20250405181650.22827-2-arkamar@atlas.cz> X-Mailer: git-send-email 2.48.1 In-Reply-To: <20250405181650.22827-1-arkamar@atlas.cz> References: <20250405181650.22827-1-arkamar@atlas.cz> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Xen PV guests in DomU have APIC disabled by design, which causes topology_apply_cmdline_limits_early() to limit the number of possible CPUs to 1, regardless of the configured number of vCPUs. This is a regression introduced in version 6.9 in commit 7c0edad3643f ("x86/cpu/topology: Rework possible CPU management") which added an early check that limits CPUs if apic_is_disabled, without accounting for the fact that Xen PV guests always disable APIC even when SMP is supported. This patch fixes the issue by skipping the apic_is_disabled check for Xen PV guests, allowing them to boot with the full set of configured vCPUs. 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 Van=C4=9Bk --- arch/x86/kernel/cpu/topology.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/topology.c b/arch/x86/kernel/cpu/topology.c index 01456236a6dd..10aa7f471ec9 100644 --- a/arch/x86/kernel/cpu/topology.c +++ b/arch/x86/kernel/cpu/topology.c @@ -428,8 +428,13 @@ void __init topology_apply_cmdline_limits_early(void) { unsigned int possible =3D nr_cpu_ids; =20 - /* 'maxcpus=3D0' 'nosmp' 'nolapic' */ - if (!setup_max_cpus || apic_is_disabled) + /* 'maxcpus=3D0' 'nosmp' 'nolapic' + * + * The apic_is_disabled check is ignored for Xen PV domains because Xen + * disables ACPI in unprivileged PV DomU guests, which would otherwise li= mit + * CPUs to 1, even if multiple vCPUs were configured. + */ + if (!setup_max_cpus || (!xen_pv_domain() && apic_is_disabled)) possible =3D 1; =20 /* 'possible_cpus=3DN' */ --=20 2.48.1