[xen master] arm/mpu: Implement early_fdt_map support in MPU systems

[patchbot@xxxxxxx]

commit 530fb01a4ad298a5f2d3077edbc2c4e334ac9c7e
Author:     Luca Fancellu <luca.fancellu@xxxxxxx>
AuthorDate: Mon Jul 21 09:31:46 2025 +0100
Commit:     Michal Orzel <michal.orzel@xxxxxxx>
CommitDate: Wed Jul 23 09:51:55 2025 +0200

    arm/mpu: Implement early_fdt_map support in MPU systems
    
    Implement the function early_fdt_map(), which is responsible for mapping
    the Device Tree Blob in the early stages of the boot process, for MPU
    systems.
    
    We make use of the map_pages_to_xen() and destroy_xen_mappings() APIs.
    In particular the latter function is necessary in the case that the
    initial mapping of the fdt_header is insufficient to cover the entire
    DTB, as we must destroy and then remap the region due to the APIs no
    providing support for extending the size of an existing region.
    
    Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
    Signed-off-by: Hari Limaye <hari.limaye@xxxxxxx>
    Reviewed-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
    Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>
---
 xen/arch/arm/mpu/setup.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 71 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/mpu/setup.c b/xen/arch/arm/mpu/setup.c
index b4da77003f..2ef703757f 100644
--- a/xen/arch/arm/mpu/setup.c
+++ b/xen/arch/arm/mpu/setup.c
@@ -1,17 +1,86 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#include <xen/bootfdt.h>
 #include <xen/bug.h>
 #include <xen/init.h>
+#include <xen/libfdt/libfdt.h>
 #include <xen/mm.h>
+#include <xen/pfn.h>
 #include <xen/types.h>
+#include <xen/sizes.h>
 #include <asm/setup.h>
 
+static paddr_t __initdata mapped_fdt_base = INVALID_PADDR;
+static paddr_t __initdata mapped_fdt_limit = INVALID_PADDR;
+
 void __init setup_pagetables(void) {}
 
 void * __init early_fdt_map(paddr_t fdt_paddr)
 {
-    BUG_ON("unimplemented");
-    return NULL;
+    /* Map at least a page containing the DTB address, exclusive range */
+    paddr_t base = round_pgdown(fdt_paddr);
+    paddr_t limit = round_pgup(fdt_paddr + sizeof(struct fdt_header));
+    unsigned int flags = PAGE_HYPERVISOR_RO;
+    void *fdt_virt = (void *)fdt_paddr; /* virt == paddr for MPU */
+    int rc;
+    uint32_t size;
+    unsigned long nr_mfns;
+
+    /*
+     * Check whether the physical FDT address is set and meets the minimum
+     * alignment requirement. Since we are relying on MIN_FDT_ALIGN to be at
+     * least 8 bytes so that we always access the magic and size fields
+     * of the FDT header after mapping the first chunk, double check if
+     * that is indeed the case.
+     */
+    BUILD_BUG_ON(MIN_FDT_ALIGN < 8);
+    if ( !fdt_paddr || fdt_paddr % MIN_FDT_ALIGN )
+        return NULL;
+
+    /*
+     * DTB at this address has already been mapped.`start_xen` calls this 
twice,
+     * before and after `setup_page_tables`, which is a no-op on MPU.
+     */
+    if ( mapped_fdt_base == fdt_paddr )
+        return fdt_virt;
+
+    ASSERT(mapped_fdt_base == INVALID_PADDR);
+
+    nr_mfns = (limit - base) >> PAGE_SHIFT;
+
+    rc = map_pages_to_xen(base, maddr_to_mfn(base), nr_mfns, flags);
+    if ( rc )
+        panic("Unable to map the device-tree\n");
+
+    mapped_fdt_base = fdt_paddr;
+    mapped_fdt_limit = limit;
+
+    if ( fdt_magic(fdt_virt) != FDT_MAGIC )
+        return NULL;
+
+    size = fdt_totalsize(fdt_virt);
+    if ( size > MAX_FDT_SIZE )
+        return NULL;
+
+    limit = round_pgup(fdt_paddr + size);
+
+    /* If the mapped range is not enough, map the rest of the DTB. */
+    if ( limit > mapped_fdt_limit )
+    {
+        rc = destroy_xen_mappings(base, mapped_fdt_limit);
+        if ( rc )
+            panic("Unable to unmap the device-tree header\n");
+
+        nr_mfns = (limit - base) >> PAGE_SHIFT;
+
+        rc = map_pages_to_xen(base, maddr_to_mfn(base), nr_mfns, flags);
+        if ( rc )
+            panic("Unable to map the device-tree\n");
+
+        mapped_fdt_limit = limit;
+    }
+
+    return fdt_virt;
 }
 
 /*
--
generated by git-patchbot for /home/xen/git/xen.git#master