From 312b5687c905a7614cdd1e5080a69bd12cbc95b4 Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Sun, 2 Jun 2024 21:42:28 -0400
Subject: kernel/amd64: pmap: Add helper to set cache policy

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 sys/arch/amd64/amd64/pmap.c | 32 ++++++++++++++++++++++++++++++++
 sys/include/vm/pmap.h       | 10 ++++++++++
 2 files changed, 42 insertions(+)

diff --git a/sys/arch/amd64/amd64/pmap.c b/sys/arch/amd64/amd64/pmap.c
index e95471b..9443727 100644
--- a/sys/arch/amd64/amd64/pmap.c
+++ b/sys/arch/amd64/amd64/pmap.c
@@ -254,6 +254,38 @@ pmap_modify_tbl(struct vm_ctx *ctx, struct vas vas, vaddr_t va, size_t val)
     return 0;
 }
 
+int
+pmap_set_cache(struct vm_ctx *ctx, struct vas vas, vaddr_t va, int type)
+{
+    uintptr_t *tbl;
+    int status;
+    size_t idx;
+
+    if ((status = pmap_get_tbl(ctx, vas, va, false, &tbl)) != 0) {
+        return status;
+    }
+
+    idx = pmap_get_level_index(1, va);
+
+    /* Set the policy based on the type */
+    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:
+        /* Invalid type */
+        return 1;
+    }
+
+    pmap_flush(va);
+    return 0;
+}
+
 int
 pmap_map(struct vm_ctx *ctx, struct vas vas, vaddr_t va, paddr_t pa,
          vm_prot_t prot)
diff --git a/sys/include/vm/pmap.h b/sys/include/vm/pmap.h
index 8c69372..cb18885 100644
--- a/sys/include/vm/pmap.h
+++ b/sys/include/vm/pmap.h
@@ -54,6 +54,10 @@
 #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 */
+
 #define is_vas_valid(vas) (vas.top_level != 0)
 
 /*
@@ -66,6 +70,12 @@ struct vm_ctx {
     struct spinlock dynalloc_lock;
 };
 
+/*
+ * Mark a virtual address with a specific caching
+ * type.
+ */
+int pmap_set_cache(struct vm_ctx *, struct vas, vaddr_t, int);
+
 /*
  * Create a virtual address space
  * and return the descriptor.
-- 
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