[RFC PATCH 02/37] KVM: MMU: Move struct kvm_mmu_page_role into common code

[Paolo Bonzini]

On 12/8/22 20:38, David Matlack wrote:
> +/*
> + * kvm_mmu_page_role tracks the properties of a shadow page (where shadow page
> + * also includes TDP pages) to determine whether or not a page can be used in
> + * the given MMU context.
> + */
> +union kvm_mmu_page_role {
> +	u32 word;
> +	struct {
> +		struct {
> +			/* The address space ID mapped by the page. */
> +			u16 as_id:8;
> +
> +			/* The level of the page in the page table hierarchy. */
> +			u16 level:4;
> +
> +			/* Whether the page is invalid, i.e. pending destruction. */
> +			u16 invalid:1;
> +		};
> +
> +		/* Architecture-specific properties. */
> +		struct kvm_mmu_page_role_arch arch;
> +	};
> +};
> +

Have you considered adding a tdp_mmu:1 field to the arch-independent 
part?  I think that as long as _that_ field is the same, there's no need 
to have any overlap between TDP MMU and shadow MMU roles.

I'm not even sure if the x86 TDP MMU needs _any_ other role bit.  It 
needs of course the above three, and it also needs "direct" but it is 
used exactly to mean "is this a TDP MMU page".  So we could have

union {
	struct {
		u32 tdp_mmu:1;
		u32 invalid:1;
		u32 :6;
		u32 level:8;
		u32 arch:8;
		u32 :8;
	} tdp;
	/* the first field must be "u32 tdp_mmu:1;" */
	struct kvm_mmu_page_role_arch shadow;
};

Paolo