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

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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

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