KVM: x86/mmu: Truncate paging32's PT_BASE_ADDR_MASK to 32 bits

Truncate paging32's PT_BASE_ADDR_MASK to a pt_element_t, i.e. to 32 bits.
Ignoring PSE huge pages, the mask is only used in conjunction with gPTEs,
which are 32 bits, and so the address is limited to bits 31:12.

PSE huge pages encoded PA bits 39:32 in PTE bits 20:13, i.e. need custom
logic to handle their funky encoding regardless of PT_BASE_ADDR_MASK.

Note, PT_LVL_OFFSET_MASK is somewhat confusing in that it computes the
offset of the _gfn_, not of the gpa, i.e. not having bits 63:32 set in
PT_BASE_ADDR_MASK is again correct.

No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220614233328.3896033-8-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/paging_tmpl.h

@@ -39,7 +39,7 @@
 	#define pt_element_t u32
 	#define guest_walker guest_walker32
 	#define FNAME(name) paging##32_##name
-	#define PT_BASE_ADDR_MASK PAGE_MASK
+	#define PT_BASE_ADDR_MASK ((pt_element_t)PAGE_MASK)
 	#define PT_LEVEL_BITS 10
 	#define PT_MAX_FULL_LEVELS 2
 	#define PT_GUEST_DIRTY_SHIFT PT_DIRTY_SHIFT