From 26d9b8d6f3617c1d466ca8d3b28f368fdf25e29a Mon Sep 17 00:00:00 2001
From: Luke Craig <lacraig3@gmail.com>
Date: Wed, 3 Jun 2026 12:09:33 -0400
Subject: [PATCH] Map QEMU mmap apertures as normal memory on arm64

---
 src/portal/portal_anon.c   |  5 +++--
 src/portal/portal_devfs.c  |  3 ++-
 src/portal/portal_mmap.h   | 20 ++++++++++++++++++++
 src/portal/portal_procfs.c |  3 ++-
 4 files changed, 27 insertions(+), 4 deletions(-)
 create mode 100644 src/portal/portal_mmap.h

diff --git a/src/portal/portal_anon.c b/src/portal/portal_anon.c
index e92259c..8b09683 100644
--- a/src/portal/portal_anon.c
+++ b/src/portal/portal_anon.c
@@ -4,6 +4,7 @@
 #include <linux/net.h>
 #include <linux/file.h>
 #include "portal_devfs.h"
+#include "portal_mmap.h"
 
 
 struct portal_anonfs_create_req {
@@ -44,7 +45,7 @@ static int igloo_anonfs_proxy_mmap(struct file *file, struct vm_area_struct *vma
     size_t size = vma->vm_end - vma->vm_start;
 
     if (pe && pe->mmap_phys_addr) {
-        vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+        vma->vm_page_prot = igloo_mmap_phys_pgprot(vma->vm_page_prot);
         return remap_pfn_range(vma, vma->vm_start, pe->mmap_phys_addr >> PAGE_SHIFT,
                                size, vma->vm_page_prot);
     }
@@ -205,4 +206,4 @@ void handle_op_sockfs_create_socket(portal_region *mem_region) {
 
 fail:
     mem_region->header.op = HYPER_RESP_WRITE_FAIL;
-}
\ No newline at end of file
+}
diff --git a/src/portal/portal_devfs.c b/src/portal/portal_devfs.c
index f341ee1..1db00ea 100644
--- a/src/portal/portal_devfs.c
+++ b/src/portal/portal_devfs.c
@@ -20,6 +20,7 @@
 #include <linux/blk-mq.h>
 
 #include "portal_devfs.h"
+#include "portal_mmap.h"
 
 // Request to create a directory in devfs
 struct portal_devfs_dir_req {
@@ -225,7 +226,7 @@ static int igloo_devfs_proxy_mmap(struct file *file, struct vm_area_struct *vma)
 
     if (pe->mmap_phys_addr) {
         // NATIVE QEMU MMAP: Directly map the physical address assigned by Penguin
-        vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+        vma->vm_page_prot = igloo_mmap_phys_pgprot(vma->vm_page_prot);
         return remap_pfn_range(vma, vma->vm_start, pe->mmap_phys_addr >> PAGE_SHIFT,
                                size, vma->vm_page_prot);
     }
diff --git a/src/portal/portal_mmap.h b/src/portal/portal_mmap.h
new file mode 100644
index 0000000..d153d20
--- /dev/null
+++ b/src/portal/portal_mmap.h
@@ -0,0 +1,20 @@
+#ifndef IGLOO_PORTAL_MMAP_H
+#define IGLOO_PORTAL_MMAP_H
+
+#include <linux/mm.h>
+
+static inline pgprot_t igloo_mmap_phys_pgprot(pgprot_t prot)
+{
+#if defined(CONFIG_ARM64)
+    /*
+     * arm64 maps pgprot_noncached() as device memory. User-space string and
+     * runtime helpers may issue unaligned accesses into mmap()ed pseudo-files,
+     * and device mappings fault on those accesses before QEMU sees the MMIO.
+     */
+    return pgprot_writecombine(prot);
+#else
+    return pgprot_noncached(prot);
+#endif
+}
+
+#endif
diff --git a/src/portal/portal_procfs.c b/src/portal/portal_procfs.c
index f8d0070..9bfc6dd 100644
--- a/src/portal/portal_procfs.c
+++ b/src/portal/portal_procfs.c
@@ -18,6 +18,7 @@
 
 #include "../args.h"
 #include "portal_procfs.h"
+#include "portal_mmap.h"
 
 #if LINUX_VERSION_CODE >= KERNEL_VERSION(6,13,0)
 #define IGLOO_NEEDS_PROC_PERMANENT_CLEAR 1
@@ -103,7 +104,7 @@ int igloo_proxy_mmap(struct file *file, struct vm_area_struct *vma)
 
     if (pe->mmap_phys_addr) {
         // NATIVE QEMU MMAP: Directly map the physical address assigned by Penguin
-        vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
+        vma->vm_page_prot = igloo_mmap_phys_pgprot(vma->vm_page_prot);
         return remap_pfn_range(vma, vma->vm_start, pe->mmap_phys_addr >> PAGE_SHIFT,
                                size, vma->vm_page_prot);
     }