Re: [PATCH v3 18/40] KVM: x86: Move kvm_caps and kvm_host_values to asm/kvm_host.h

[Yosry Ahmed]

On Fri, May 29, 2026 at 03:22:01PM -0700, Sean Christopherson wrote:
> Relocate the kvm_caps and kvm_host_values struct definitions and their
> associated global variable declarations to asm/kvm_host.h to allow for a
> variety of cleanups in x86.h and mmu.h, and to establish a (hopefully)
> maintainable rule that asm/kvm_host.h's role is to define common
> structures (and declare any associated globals), and anything needed by
> arch-neutral KVM.
> 
> While it would be lovely to trim kvm_host.h down to the point where it
> *only* holds things needed by arch-neutral and/or non-KVM code, multiple
> attempts to do just that have failed miserably.  Trying to "hide" code
> from arch-neutral KVM is too restrictive (and ultimately pointless), and
> KVM x86 itself also needs a place to define common structures and their
> globals, e.g. to avoid inconsistent header include chains and/or misplaced
> helpers.
> 
> E.g. as pointed out by Kai, it's weird that x86.h, which is a kitchen sink
> of sorts, includes regs.h, but not mmu.h.  Literally the only reason that
> x86.h doesn't include mmu.h is that mmu.h references struct kvm_host, which
> is currently defined in x86.h.  As a result of odd include ordering, the
> very clearly MMU-specific helper mmu_is_nested() lives in x86.h, not mmu.h
> 
> "Fix" the kvm_host dependency so that x86.h can be the "central" include
> everyone expects it to be, and set KVM x86 on the path to having somewhat
> sensible "rules" for what goes where:
> 
>   - asm/kvm_host.h holds "common" structure definitions and associated key
>     global  variables, and things that are referenced by arch-neutral KVM.
>   - <thing>.{c,h} holds relevant declarations and definitions.
>   - x86.{c,h} is the kitchen sink for everything else.
> 
> Cc: Kai Huang <kai.huang@xxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>

Reviewed-by: Yosry Ahmed <yosry@xxxxxxxxxx>