linux-kernel - Re: [PATCH v2 08/25] KVM: x86/mmu: split cpu_mode from mmu

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Date:   Wed, 9 Mar 2022 15:38:39 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        dmatlack@...gle.com
Subject: Re: [PATCH v2 08/25] KVM: x86/mmu: split cpu_mode from mmu_role

On Wed, Mar 09, 2022, Paolo Bonzini wrote:
> On 3/8/22 19:55, Sean Christopherson wrote:
> > >   static void shadow_mmu_init_context(struct kvm_vcpu *vcpu, struct kvm_mmu *context,
> > > -				    const struct kvm_mmu_role_regs *regs,
> > > -				    union kvm_mmu_role new_role)
> > > +				    union kvm_mmu_role cpu_mode,
> > Can you give all helpers this treatment (rename "role" => "cpu_mode")?  I got
> > tripped up a few times reading patches because the ones where it wasn't necessary,
> > i.e. where there's only a single kvm_mmu_role paramenter, were left as-is.
> > 
> > I think kvm_calc_shadow_npt_root_page_role() and kvm_calc_shadow_mmu_root_page_role()
> > are the only offenders.
> 
> These take struct kvm_mmu_role_regs; they *return* union kvm_mmu_role but
> that is changed later in the series to the base part only.

Doh, sorry, a later patch is what confused me.  Lost track of things when moving
around in the series.

Patch 12, "KVM: x86/mmu: cleanup computation of MMU roles for shadow paging", is
where we end up with

	static union kvm_mmu_role
	kvm_calc_shadow_mmu_root_page_role(struct kvm_vcpu *vcpu,
					   union kvm_mmu_role role)
	{
		if (!role.ext.efer_lma)
			role.base.level = PT32E_ROOT_LEVEL;
		else if (role.ext.cr4_la57)
			role.base.level = PT64_ROOT_5LEVEL;
		else
			role.base.level = PT64_ROOT_4LEVEL;

		return role;
	}

Can we instead tweak that patch to make it and kvm_calc_shadow_npt_root_page_role() be

	static union kvm_mmu_role
	kvm_calc_shadow_mmu_root_page_role(struct kvm_vcpu *vcpu,
					union kvm_mmu_role cpu_role)
	{
		union kvm_mmu_role root_role = cpu_role;

		if (!cpu_role.ext.efer_lma)
			root_role.base.level = PT32E_ROOT_LEVEL;
		else if (cpu_role.ext.cr4_la57)
			root_role.base.level = PT64_ROOT_5LEVEL;
		else
			root_role.base.level = PT64_ROOT_4LEVEL;

		return root_role;
	}

This is effectively the same feedback I gave in Patch 15[*], I messed up when
trying to track back where the "union kvm_mmu_role role" param was introduced.

https://lore.kernel.org/all/YieoXYBFyo9pZhhX@google.com