Re: [PATCH 11/15] KVM: arm64: Use debug_owner to track if debug regs need save/restore

[Oliver Upton <oliver.upton@linux.dev>]

On Sat, Nov 09, 2024 at 12:11:39PM +0000, Marc Zyngier wrote:
> >  static bool trap_debug_regs(struct kvm_vcpu *vcpu,
> >  			    struct sys_reg_params *p,
> >  			    const struct sys_reg_desc *r)
> >  {
> >  	access_rw(vcpu, p, r);
> >  	if (p->is_write)
> > -		vcpu_set_flag(vcpu, DEBUG_DIRTY);
> >
> >  	kvm_handle_debug_access(vcpu);
> 
> Something has gone wrong here, and I don't think you wanted to make
> the ownership conditional on the access being only a write.

That's very much intentional (probably not clear enough in changelog). I
don't think there's any value in special-casing this to writes.

If memory serves, Windows saves/restores the entire set of debug registers
rather frequently, and imposing a read trap storm on the save implementation
feels like a waste of cycles.

-- 
Thanks,
Oliver