linux-kernel - Re: [PATCH v2 16/25] KVM: x86/mmu: rename kvm_mmu

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Date:   Tue, 8 Mar 2022 19:15:40 +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 16/25] KVM: x86/mmu: rename kvm_mmu_role union

On Mon, Feb 21, 2022, Paolo Bonzini wrote:
> It is quite confusing that the "full" union is called kvm_mmu_role
> but is used for the "cpu_mode" field of struct kvm_mmu.  Rename it
> to kvm_mmu_paging_mode.

My official vote is to use

	union kvm_mmu_cpu_role cpu_role

instead of

	union kvm_mmu_paging_mode cpu_mode

The latter has too many inconsistencies, e.g. helpers using "role" instead of "mode",
the union using "paging" but the field/params using "cpu".  The cpu instead of paging
thing isn't a coincidence as having the param be "paging_mode" would be really, really
confusing (ditto for kvm_calc_paging_mode()).

IMO this is consistent, if imperfect.

static union kvm_mmu_cpu_role kvm_calc_cpu_role(struct kvm_vcpu *vcpu,
						const struct kvm_mmu_role_regs *regs)
{
	union kvm_mmu_cpu_role role = {0};

	role.base.access = ACC_ALL;
	role.base.smm = is_smm(vcpu);
	role.base.guest_mode = is_guest_mode(vcpu);
	role.base.direct = !____is_cr0_pg(regs);

	role.ext.valid = 1;

	if (!____is_cr0_pg(regs))
		return role;

	...

	return role;
}

Whereas this is inconsistent, and also imperfect.

static union kvm_mmu_paging_mode kvm_calc_cpu_mode(struct kvm_vcpu *vcpu,
						   const struct kvm_mmu_role_regs *regs)
{
	union kvm_mmu_paging_mode role = {0};

	role.base.access = ACC_ALL;
	role.base.smm = is_smm(vcpu);
	role.base.guest_mode = is_guest_mode(vcpu);
	role.base.direct = !____is_cr0_pg(regs);

	role.ext.valid = 1;

	if (!____is_cr0_pg(regs))
		return role;

	...

	return role;
}