vm: allow pages to be mapped as no-cache

arch/x86_64/pmap.c

@@ -71,6 +71,10 @@ static pte_t make_pte(pfn_t pfn, enum vm_prot prot, enum page_size size)
 		v |= PTE_RW;
 	}
 
+	if (prot & VM_PROT_NOCACHE) {
+		v |= PTE_NOCACHE;
+	}
+
 	if (!(prot & VM_PROT_EXEC)) {
 		v |= PTE_NX;
 	}
@@ -267,7 +271,7 @@ void pmap_bootstrap(void)
 		do_pmap_add(kernel_pmap,
 			    (void *)(vbase + i),
 			    PFN(i),
-			    VM_PROT_READ | VM_PROT_WRITE | VM_PROT_SVR, hugepage);
+			    VM_PROT_READ | VM_PROT_WRITE | VM_PROT_SVR | VM_PROT_NOCACHE, hugepage);
 	}
 
 	pmap_switch(kernel_pmap);

include/socks/vm.h

@@ -47,6 +47,7 @@ enum vm_prot {
 	VM_PROT_EXEC    = 0x04u,
 	VM_PROT_USER    = 0x08u,
 	VM_PROT_SVR     = 0x10u,
+	VM_PROT_NOCACHE = 0x20u,
 };
 
 enum vm_flags {