linux-kernel - Re: [PATCH 1/2] x86/xen: add CPU dependencies for 32-bit build

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Message-ID: <df186d0d-3178-48fe-a633-3b8f8016f5cf@suse.com>
Date:   Mon, 4 Dec 2023 13:59:31 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Arnd Bergmann <arnd@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Cc:     Arnd Bergmann <arnd@...db.de>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        "H. Peter Anvin" <hpa@...or.com>, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] x86/xen: add CPU dependencies for 32-bit build

On 04.12.23 09:47, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.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@...db.de>

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen


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