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

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Date:   Wed, 2 Aug 2023 08:49:00 +0200
From:   Philippe Mathieu-Daudé <philmd@...aro.org>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, 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

On 2/8/23 01:41, Sean Christopherson wrote:
> On Tue, Aug 01, 2023, Philippe Mathieu-Daudé wrote:
>> 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> ?
> 
> It's indirectly included via
> 
>    linux/kvm_host.h => linux/bug.h => linux/build_bug.h
> 
> Depending on the day, I might argue for explicitly including all dependencies, but
> in this case build_bug.h is a "core" header, and IMO there's no value added by
> including it directly.

OK, fine then, thanks!