[xen staging] xen/arm64: Panic if direct map is too small

[patchbot@xxxxxxx]

commit 9fc76a2e35f183dee961f4b768f0af6df7459ccf
Author:     Michal Orzel <michal.orzel@xxxxxxx>
AuthorDate: Fri Jul 4 09:54:27 2025 +0200
Commit:     Stefano Stabellini <stefano.stabellini@xxxxxxx>
CommitDate: Mon Jul 7 15:09:01 2025 -0700

    xen/arm64: Panic if direct map is too small
    
    Harden the code by panicing if direct map is too small for current memory
    layout taking into account possible PDX compression. Otherwise the assert
    is observed:
    Assertion '(mfn_to_pdx(maddr_to_mfn(ma)) - directmap_base_pdx) < 
(DIRECTMAP_SIZE >> PAGE_SHIFT)' failed at ./arch/arm/include/asm/mmu/mm.h:72
    
    At the moment, we don't set max_pdx denoting maximum usable PDX which
    should be based on max_page. Consolidate setting of max_page and max_pdx
    in init_pdx() for both arm32 and arm64. max_pdx will be used in the
    future to set up frametable mappings respecting the PDX grouping.
    
    Signed-off-by: Michal Orzel <michal.orzel@xxxxxxx>
    Reviewed-by: Hari Limaye <hari.limaye@xxxxxxx>
    Tested-by: Hari Limaye <hari.limaye@xxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
---
 xen/arch/arm/arm32/mmu/mm.c | 1 -
 xen/arch/arm/arm64/mmu/mm.c | 4 +++-
 xen/arch/arm/setup.c        | 6 +++++-
 3 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/xen/arch/arm/arm32/mmu/mm.c b/xen/arch/arm/arm32/mmu/mm.c
index 4d22f35618..e6d9b49acd 100644
--- a/xen/arch/arm/arm32/mmu/mm.c
+++ b/xen/arch/arm/arm32/mmu/mm.c
@@ -190,7 +190,6 @@ void __init setup_mm(void)
 
     /* Frame table covers all of RAM region, including holes */
     setup_frametable_mappings(ram_start, ram_end);
-    max_page = PFN_DOWN(ram_end);
 
     /*
      * The allocators may need to use map_domain_page() (such as for
diff --git a/xen/arch/arm/arm64/mmu/mm.c b/xen/arch/arm/arm64/mmu/mm.c
index a0a2dd8cc7..3e64be6ae6 100644
--- a/xen/arch/arm/arm64/mmu/mm.c
+++ b/xen/arch/arm/arm64/mmu/mm.c
@@ -224,6 +224,9 @@ static void __init setup_directmap_mappings(unsigned long 
base_mfn,
          */
         directmap_virt_start = DIRECTMAP_VIRT_START +
             (base_mfn - mfn_gb) * PAGE_SIZE;
+
+        if ( (max_pdx - directmap_base_pdx) > (DIRECTMAP_SIZE >> PAGE_SHIFT) )
+            panic("Direct map is too small\n");
     }
 
     if ( base_mfn < mfn_x(directmap_mfn_start) )
@@ -278,7 +281,6 @@ void __init setup_mm(void)
     directmap_mfn_end = maddr_to_mfn(ram_end);
 
     setup_frametable_mappings(ram_start, ram_end);
-    max_page = PFN_DOWN(ram_end);
 
     init_staticmem_pages();
     init_sharedmem_pages();
diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index 58acc2d0d4..93b730ffb5 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -254,7 +254,7 @@ static void __init relocate_fdt(const void **dtb_vaddr, 
size_t dtb_size)
 void __init init_pdx(void)
 {
     const struct membanks *mem = bootinfo_get_mem();
-    paddr_t bank_start, bank_size, bank_end;
+    paddr_t bank_start, bank_size, bank_end, ram_end = 0;
 
     /*
      * Arm does not have any restrictions on the bits to compress. Pass 0 to
@@ -290,10 +290,14 @@ void __init init_pdx(void)
         bank_start = mem->bank[bank].start;
         bank_size = mem->bank[bank].size;
         bank_end = bank_start + bank_size;
+        ram_end = max(ram_end, bank_end);
 
         set_pdx_range(paddr_to_pfn(bank_start),
                       paddr_to_pfn(bank_end));
     }
+
+    max_page = PFN_DOWN(ram_end);
+    max_pdx = pfn_to_pdx(max_page - 1) + 1;
 }
 
 size_t __read_mostly dcache_line_bytes;
--
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