Map QEMU mmap apertures as normal memory on arm64

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;
-}
+}

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);
     }

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

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);
     }