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@amd.com>
Reviewed-by: Hari Limaye <hari.limaye@arm.com>
Tested-by: Hari Limaye <hari.limaye@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

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

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();

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;