2023-07-29 00:56:00

by Sean Christopherson

Subject: [PATCH v3 10/12] KVM: x86/mmu: Use BUILD_BUG_ON_INVALID() for KVM_MMU_WARN_ON() stub

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 <[email protected]>
---
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)
#endif

/* Page table builder macros common to shadow (host) PTEs and guest PTEs. */
--
2.41.0.487.g6d72f3e995-goog

2023-08-01 15:55:17

by Philippe Mathieu-Daudé

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 <[email protected]>
> ---
> 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 <[email protected]>

> #endif
>

2023-08-02 02:01:14

by Sean Christopherson

Subject: Re: [PATCH v3 10/12] KVM: x86/mmu: Use BUILD_BUG_ON_INVALID() for KVM_MMU_WARN_ON() stub

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 <[email protected]>
> > ---
> > 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.

2023-08-02 07:53:34

by Philippe Mathieu-Daudé

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 <[email protected]>
>>> ---
>>> 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!