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From:   Arnd Bergmann <arnd@kernel.org>
To:     Juergen Gross <jgross@suse.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Boris Ostrovsky <boris.ostrovsky@oracle.com>,
        "H. Peter Anvin" <hpa@zytor.com>, xen-devel@lists.xenproject.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH 1/2] x86/xen: add CPU dependencies for 32-bit build
Date:   Mon,  4 Dec 2023 09:47:01 +0100
Message-Id: <20231204084722.3789473-1-arnd@kernel.org>
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From: Arnd Bergmann <arnd@arndb.de>

Xen only supports modern CPUs even when running a 32-bit kernel, and it now
requires a kernel built for a 64 byte (or larger) cache line:

In file included from <command-line>:
In function 'xen_vcpu_setup',
    inlined from 'xen_vcpu_setup_restore' at arch/x86/xen/enlighten.c:111:3,
    inlined from 'xen_vcpu_restore' at arch/x86/xen/enlighten.c:141:3:
include/linux/compiler_types.h:435:45: error: call to '__compiletime_assert_287' declared with attribute error: BUILD_BUG_ON failed: sizeof(*vcpup) > SMP_CACHE_BYTES
arch/x86/xen/enlighten.c:166:9: note: in expansion of macro 'BUILD_BUG_ON'
  166 |         BUILD_BUG_ON(sizeof(*vcpup) > SMP_CACHE_BYTES);
      |         ^~~~~~~~~~~~

Enforce the dependency with a whitelist of CPU configurations. In normal
distro kernels, CONFIG_X86_GENERIC is enabled, and this works fine. When this
is not set, still allow Xen to be built on kernels that target a 64-bit
capable CPU.

Fixes: db2832309a82 ("x86/xen: fix percpu vcpu_info allocation")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 arch/x86/xen/Kconfig | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/xen/Kconfig b/arch/x86/xen/Kconfig
index 9b1ec5d8c99c..a65fc2ae15b4 100644
--- a/arch/x86/xen/Kconfig
+++ b/arch/x86/xen/Kconfig
@@ -9,6 +9,7 @@ config XEN
 	select PARAVIRT_CLOCK
 	select X86_HV_CALLBACK_VECTOR
 	depends on X86_64 || (X86_32 && X86_PAE)
+	depends on X86_64 || (X86_GENERIC || MPENTIUM4 || MCORE2 || MATOM || MK8)
 	depends on X86_LOCAL_APIC && X86_TSC
 	help
 	  This is the Linux Xen port.  Enabling this will allow the
-- 
2.39.2