Subject: Re: linux-next: Tree for Mar 25 (arch/x86/kvm/)

From: Sean Christopherson <[email-masked]>
Date: Wed, 25 Mar 2020 09:46:06 -0700

On Wed, Mar 25, 2020 at 05:26:20PM +0100, Paolo Bonzini wrote:
> On 25/03/20 17:14, Sean Christopherson wrote:
> >> Doh, right.  I think the only solution for that one is to degrade it to
> >> WARN_ON(1).
> > I reproduced the error, give me a bit to play with the code to see if the
> > BUILD_BUG can be preserved.  I'm curious as to why kvm_cpu_cap_mask() is
> > special, and why it only fails with this config.
> > 
> 
> I could not reproduce it, but I would not be surprised if there are
> other configurations where the compiler cannot constant-propagate from
> the reverse_cpuid struct into __cpuid_entry_get_reg.

The error is related to UBSAN.  There is at least one legitimate (but benign)
underlying issue.  I'm chasing down a second instance of the BUILD_BUG.

Assuming all issues can be fixed, I think it'd make sense to keep the
BUILD_BUG, especially if it's teasing out actual weirdness, even if the
weirdness is benign.