[Xen-devel] [PATCH V2] Revert "xen/arm: do not relocate Xen outside of visible RAM"

[Sameer Goel <sgoel@xxxxxxxxxxxxxx>]

This reverts commit db92b1ac55cd5e193ae22b0b6f01fb47bc9e5d2f.

The restriction on non contiguous memory was resolved by commit
2d02b05c77fc5e7c76bf6f112db84bbaa44fdcb5:
"xen: arm: improve handling of system with non-contiguous RAM regions"

So, reverting this change,to enable Xen image placement at the end of the
useable system RAM.

Signed-off-by: Sameer Goel <sgoel@xxxxxxxxxxxxxx>
---
The load restriction placed in the above reverted patch resulted in a crash
when booting DOM0 on a Qualcomm platform with non contiguous system RAM.

(XEN) DOM0: [ 0.000000] bootmem alloc of 64 bytes failed!
(XEN) DOM0: [ 0.000000] Kernel panic - not syncing: Out of memory
(XEN) DOM0: [ 0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.7.0-rc7+ #19
(XEN) DOM0: [ 0.000000] Hardware name: (null) (DT)
(XEN) DOM0: [ 0.000000] Call trace:
(XEN) DOM0: [ 0.000000] [<ffff000008088854>] dump_backtrace+0x0/0x1e4
(XEN) DOM0: [ 0.000000] [<ffff000008088a5c>] show_stack+0x24/0x2c
(XEN) DOM0: [ 0.000000] [<ffff000008452004>] dump_stack+0x8c/0xb0
(XEN) DOM0: [ 0.000000] [<ffff00000819ee78>] panic+0x128/0x268
(XEN) DOM0: [ 0.000000] [<ffff00000902c018>] __alloc_bootmem_low+0x40/0x4c
(XEN) DOM0: [ 0.000000] [<ffff000009012adc>] setup_arch+0x2d8/0x560
(XEN) DOM0: [ 0.000000] [<ffff00000901084c>] start_kernel+0x60/0x3b4
(XEN) DOM0: [ 0.000000] [<ffff0000090101bc>] __primary_switched+0x30/0x74
(XEN) DOM0: [ 0.000000] ---[ end Kernel panic - not syncing: Out of memory

The root cause for the crash was >4GB difference between the arm grant table
(lower address) and the kernel start address. The kernel sees the grant table
region as the start of system RAM.

Since, the grant table is a reuse of the text region of Xen image this issue
would not be seen if Xen is loaded high enough in memory.

 xen/arch/arm/setup.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
index 38eb888..1678871 100644
--- a/xen/arch/arm/setup.c
+++ b/xen/arch/arm/setup.c
@@ -392,25 +392,17 @@ static paddr_t __init get_xen_paddr(void)
 {
     struct meminfo *mi = &bootinfo.mem;
     paddr_t min_size;
-    paddr_t paddr = 0, last_end;
+    paddr_t paddr = 0;
     int i;
 
     min_size = (_end - _start + (XEN_PADDR_ALIGN-1)) & ~(XEN_PADDR_ALIGN-1);
 
-    last_end = mi->bank[0].start;
-
     /* Find the highest bank with enough space. */
     for ( i = 0; i < mi->nr_banks; i++ )
     {
         const struct membank *bank = &mi->bank[i];
         paddr_t s, e;
 
-        /* We can only deal with contiguous memory at the moment */
-        if ( last_end != bank->start )
-            break;
-
-        last_end = bank->start + bank->size;
-
         if ( bank->size >= min_size )
         {
             e = consider_modules(bank->start, bank->start + bank->size,
-- 
Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc. 
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux 
Foundation Collaborative Project.


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