From 727c5fb46b3b68ed1d00912e87de4874e63405cf Mon Sep 17 00:00:00 2001
From: Ian Moffett <ian@osmora.org>
Date: Tue, 16 Sep 2025 16:19:15 -0400
Subject: kern/amd64: mmu: Add routine to switch VAS

This commit introduces a new mmu_write_vas() function to allow the
caller to change the virtual address space used by the current
processor.

Signed-off-by: Ian Moffett <ian@osmora.org>
---
 src/sys/arch/amd64/cpu/mmu.c | 30 ++++++++++++++++++++++++++++++
 src/sys/include/vm/mmu.h     | 11 +++++++++++
 2 files changed, 41 insertions(+)

(limited to 'src')

diff --git a/src/sys/arch/amd64/cpu/mmu.c b/src/sys/arch/amd64/cpu/mmu.c
index 3f11781..66f8584 100644
--- a/src/sys/arch/amd64/cpu/mmu.c
+++ b/src/sys/arch/amd64/cpu/mmu.c
@@ -146,6 +146,22 @@ __mmu_read_cr3(void)
     return cr3;
 }
 
+/*
+ * Write a value to the CR3 register
+ *
+ * @cr3: Value to write
+ */
+static inline void
+__mmu_write_cr3(uint64_t val)
+{
+    __ASMV(
+        "mov %0, %%cr3"
+        :
+        : "r" (val)
+        : "memory"
+    );
+}
+
 /*
  * Acquire the paging level used by the
  * current processing element (pcore)
@@ -363,6 +379,20 @@ mmu_new_vas(struct vm_vas *res)
     return 0;
 }
 
+/*
+ * Switch the VAS
+ */
+int
+mmu_write_vas(struct vm_vas *vas)
+{
+    if (vas->cr3 == 0) {
+        return -EINVAL;
+    }
+
+    __mmu_write_cr3(vas->cr3);
+    return 0;
+}
+
 /*
  * Verify that we are in a known state
  */
diff --git a/src/sys/include/vm/mmu.h b/src/sys/include/vm/mmu.h
index 908748b..820b24d 100644
--- a/src/sys/include/vm/mmu.h
+++ b/src/sys/include/vm/mmu.h
@@ -106,4 +106,15 @@ int mmu_this_vas(struct vm_vas *vasres_p);
  */
 int mmu_new_vas(struct vm_vas *res);
 
+/*
+ * Apply a virtual address descriptor to the current
+ * process and flush out the entire TLB
+ *
+ * @vas: Virtual address space to switch to
+ *
+ * Returns zero on success, otherwise a less than zero
+ * value to indicate error.
+ */
+int mmu_write_vas(struct vm_vas *vas);
+
 #endif  /* !_MACHINE_MMU_H_ */
-- 
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