linux-kernel - Re: [PATCH v3 10/12] KVM: x86/mmu: Use BUILD_BUG_ON_INVALID() for KVM_MMU_WARN

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Date:   Tue, 1 Aug 2023 16:04:37 +0200
From:   Philippe Mathieu-Daudé <philmd@...aro.org>
To:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Mingwei Zhang <mizhang@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Jim Mattson <jmattson@...gle.com>
Subject: Re: [PATCH v3 10/12] KVM: x86/mmu: Use BUILD_BUG_ON_INVALID() for
 KVM_MMU_WARN_ON() stub

Hi Sean,

On 29/7/23 02:47, Sean Christopherson wrote:
> Use BUILD_BUG_ON_INVALID() instead of an empty do-while loop to stub out
> KVM_MMU_WARN_ON() when CONFIG_KVM_PROVE_MMU=n, that way _some_ build
> issues with the usage of KVM_MMU_WARN_ON() will be dected even if the
> kernel is using the stubs, e.g. basic syntax errors will be detected.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>   arch/x86/kvm/mmu/mmu_internal.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
> index 40e74db6a7d5..f1ef670058e5 100644
> --- a/arch/x86/kvm/mmu/mmu_internal.h
> +++ b/arch/x86/kvm/mmu/mmu_internal.h
> @@ -9,7 +9,7 @@
>   #ifdef CONFIG_KVM_PROVE_MMU
>   #define KVM_MMU_WARN_ON(x) WARN_ON_ONCE(x)
>   #else
> -#define KVM_MMU_WARN_ON(x) do { } while (0)
> +#define KVM_MMU_WARN_ON(x) BUILD_BUG_ON_INVALID(x)

No need to include <linux/build_bug.h> ? Anyhow,

Reviewed-by: Philippe Mathieu-Daudé <philmd@...aro.org>

>   #endif
>