Xen devel - Dec 2008 - pv_grub and >1023M RAM == death

pv_grub x86, when booted with more than 1023MB of RAM, will produce the 
following output:

Xen Minimal OS!
start_info:   0xa72000
   nr_pages:   276480  shared_inf: cfdca000
   pt_base:    0xa75000  mod_start:  0x0
   mod_len:    0
   flags:      0x0
   cmd_line:   (hd0)/boot/grub/menu.lst
   stack:      0x943780-0x963780
MM: Init
   _text:        0x0
   _etext:       0x5f0ca
   _erodata:     0x73000
   _edata:       0x786d4
   stack start:  0x943780
   _end:         0x963d14
   start_pfn:    a81
   max_pfn:      43800
Mapping memory range 0xc00000 - 0x43800000
setting 0x0-0x73000 readonly
skipped 0x1000
MM: Initialise page allocator for c98000(c98000)-0(43800000)
MM: done
Demand map pfns at 43801000-c3801000.
Heap resides at c3802000-3802000.
Initialising timer interface
Initialising console ... done.
gnttab_table mapped at 0x43801000.
Initialising scheduler
Heap exhausted: 0xc3802000 + 480 = 0xc3802480 > 0x3802000
Heap exhausted: 0xc3802000 + b80 = 0xc3802b80 > 0x3802000
Page fault at linear address 0x4, eip 0x519fd, regs 0x95fea8, sp 
0x77da0, our_sp 0x95fe88, code 2
Page fault in pagetable walk (access to invalid memory?).

-Chris

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Hello,

Christopher S. Aker, le Wed 03 Dec 2008 14:05:55 -0500, a écrit
:
> pv_grub x86, when booted with more than 1023MB of RAM, will produce the 
> following output:
Ah, mini-os doesn''t have any protection against that.  I don''t
have a
machine here to test, could you check the patch below?

Samuel



Clip memory not usable by Mini-OS (above 1GB)

signed-off-by: samuel.thibault@ens-lyon.org

diff -r 4c67985c552e extras/mini-os/arch/x86/mm.c
--- a/extras/mini-os/arch/x86/mm.c	Wed Nov 19 13:17:31 2008 +0000
+++ b/extras/mini-os/arch/x86/mm.c	Fri Dec 05 00:19:19 2008 +0100
@@ -420,7 +420,9 @@
 #define DEMAND_MAP_PAGES ((2ULL << 30) / PAGE_SIZE)
 #endif
 
-#ifdef HAVE_LIBC
+#ifndef HAVE_LIBC
+#define HEAP_PAGES 0
+#else
 unsigned long heap, brk, heap_mapped, heap_end;
 #ifdef __x86_64__
 #define HEAP_PAGES ((128ULL << 30) / PAGE_SIZE)
@@ -591,7 +593,7 @@
 void arch_init_mm(unsigned long* start_pfn_p, unsigned long* max_pfn_p)
 {
 
-    unsigned long start_pfn, max_pfn;
+    unsigned long start_pfn, max_pfn, virt_pfns;
 
     printk("  _text:        %p\n", &_text);
     printk("  _etext:       %p\n", &_etext);
@@ -604,7 +606,12 @@
     start_pfn = PFN_UP(to_phys(start_info.pt_base)) + 
                 start_info.nr_pt_frames + 3;
     max_pfn = start_info.nr_pages;
-   
+
+    /* We need room for demand mapping and heap, clip available memory */
+    virt_pfns = DEMAND_MAP_PAGES + HEAP_PAGES;
+    if (max_pfn + virt_pfns + 1 < max_pfn)
+        max_pfn = -(virt_pfns + 1);
+
     printk("  start_pfn:    %lx\n", start_pfn);
     printk("  max_pfn:      %lx\n", max_pfn);
 

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