kernel/amd64: Add function to set cache policy

Signed-off-by: Ian Moffett <ian@osmora.org>

2 files changed, 39 insertions, 0 deletions

diff --git a/sys/arch/amd64/amd64/pmap.c b/sys/arch/amd64/amd64/pmap.c
index 0f41e7a..1d95ec4 100644
--- a/sys/arch/amd64/amd64/pmap.c
+++ b/sys/arch/amd64/amd64/pmap.c
@@ -274,3 +274,32 @@ pmap_unmap(struct vas vas, vaddr_t va)
 {
     return pmap_update_tbl(vas, va, 0);
 }
+
+int
+pmap_set_cache(struct vas vas, vaddr_t va, int type)
+{
+    uintptr_t *tbl;
+    int status;
+    size_t idx;
+
+    if ((status = pmap_get_tbl(vas, va, false, &tbl)) != 0)
+        return status;
+
+    idx = pmap_get_level_index(1, va);
+
+    /* Set the caching policy */
+    switch (type) {
+    case VM_CACHE_UC:
+        tbl[idx] |= PTE_PCD;
+        tbl[idx] &= ~PTE_PWT;
+        break;
+    case VM_CACHE_WT:
+        tbl[idx] &= ~PTE_PCD;
+        tbl[idx] |= PTE_PWT;
+        break;
+    default:
+        return -EINVAL;
+    }
+
+    return 0;
+}
diff --git a/sys/include/vm/pmap.h b/sys/include/vm/pmap.h
index 4cd334c..741eaf2 100644
--- a/sys/include/vm/pmap.h
+++ b/sys/include/vm/pmap.h
@@ -39,6 +39,10 @@
 #define PROT_EXEC       BIT(1)      /* Executable */
 #define PROT_USER       BIT(2)      /* User accessible */
 
+/* Caching types */
+#define VM_CACHE_UC 0x00000U /* Uncachable */
+#define VM_CACHE_WT 0x00001U /* Write-through */
+
 typedef uint32_t vm_prot_t;
 
 /*
@@ -71,4 +75,10 @@ int pmap_map(struct vas vas, vaddr_t va, paddr_t pa, vm_prot_t prot);
  */
 int pmap_unmap(struct vas vas, vaddr_t va);
 
+/*
+ * Mark a virtual address with a specific
+ * caching type.
+ */
+int pmap_set_cache(struct vas vas, vaddr_t va, int type);
+
 #endif  /* !_VM_PMAP_H_ */