On Fri, May 12, 2023, David Matlack wrote: > On Thu, May 11, 2023 at 04:59:12PM -0700, Sean Christopherson wrote: > > Rename MMU_WARN_ON() to make it super obvious that the assertions are > > all about KVM's MMU, not the primary MMU. > > I think adding KVM is a step in the right direction but I have 2 > remaining problems with KVM_MMU_WARN_ON(): > > - Reminds me of VM_WARN_ON(), which toggles between WARN_ON() and > BUG_ON(), whereas KVM_MMU_WARN_ON() toggles between no-op and > WARN_ON(). No, VM_WARN_ON() bounces between WARN_ON() and nop, just like KVM_MMU_WARN_ON(). There's an extra bit of magic that adds a static assert that the code is valid (which I can/should/will add), but the runtime behavior is a nop. #define VM_WARN_ON(cond) (void)WARN_ON(cond) #else #define VM_WARN_ON(cond) BUILD_BUG_ON_INVALID(cond) /* * BUILD_BUG_ON_INVALID() permits the compiler to check the validity of the * expression but avoids the generation of any code, even if that expression * has side-effects. */ #define BUILD_BUG_ON_INVALID(e) ((void)(sizeof((__force long)(e)))) > - It's not obvious from the name that it's a no-op most of the time. > > Naming is hard so I might just make things worse by trying but... > > How about KVM_MMU_PROVE(condition). That directly pairs it with the new > CONFIG_KVM_PROVE_MMU(), makes it sufficiently different from > VM_WARN_ON() and WARN_ON() that readers will not make assumptions about > what's happening under the hood. Also "PROVE" sounds like a high bar > which conveys this might not always be enabled. It inverts the checks though. Contexting switching between "WARN_ON" and "ASSERT" is hard enough, I don't want to add a third flavor. > That also will allow us to convert this to a WARN_ON_ONCE() (my > suggestion on the other patch) without having to make the name any > longer.
