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

[Alyssa Ross <hi@xxxxxxxxx>]

On Mon, Dec 04, 2023 at 09:47:01AM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> 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@xxxxxxxx>
> ---

This fixes 32-bit distro kernel builds in Nixpkgs, which regressed
with a recent stable kernel update.  Thanks!

Tested-by: Alyssa Ross <hi@xxxxxxxxx>

>  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
>

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