savevm causes 'Bus error'

savevm causes 'Bus error'

[Jon]

Hi

I'd like to savevm/loadvm the state of my win2k virtual machine.

This works fine with qemu or with kvm using the -no-kvm switch. But
when kvm is enabled, issuing "savevm" causes a crash. All I get is the
message "Bus error" on the console.

If I try to restore a previously saved state with kvm, I get a different crash:

qemu: warning: error while loading state for instance 0x0 of device 'ram'
unhandled vm exit:  0x80000021
rax 0000000060000010 rbx 0000000000060784 rcx 00000000000000b6 rdx
0000000000307ae3
rsi 000000000000ac2f rdi 0000000006000000 rsp 0000000000067ff6 rbp
0000000000060e14
r8  0000000000000000 r9  0000000000000000 r10 0000000000000000 r11
0000000000000000
r12 0000000000000000 r13 0000000000000000 r14 0000000000000000 r15
0000000000000000
rip 00000000000003a8 rflags 00000002
cs 0058 (00020000/0000ffff p 1 dpl 0 db 0 s 1 type a l 0 g 0 avl 0)
ds 0060 (00022ac0/0000ffff p 1 dpl 0 db 0 s 1 type 2 l 0 g 0 avl 0)
es 0060 (00022ac0/0000ffff p 1 dpl 0 db 0 s 1 type 2 l 0 g 0 avl 0)
ss 0060 (00022ac0/0000ffff p 1 dpl 0 db 0 s 1 type 2 l 0 g 0 avl 0)
fs 0060 (00022ac0/0000ffff p 1 dpl 0 db 0 s 1 type 2 l 0 g 0 avl 0)
gs 0060 (00022ac0/0000ffff p 1 dpl 0 db 0 s 1 type 2 l 0 g 0 avl 0)
tr 0028 (00023ff0/00000077 p 1 dpl 0 db 0 s 0 type 9 l 0 g 0 avl 0)
ldt 0000 (00000000/00000000 p 1 dpl 0 db 0 s 0 type 0 l 0 g 0 avl 0)
gdt 36000/3ff
idt 36400/7ff
cr0 60000010 cr2 0 cr3 30000 cr4 0 cr8 0 efer 0
cirrus_vga_load: REAL_VRAM_SIZE MISMATCH !!!!!! SAVED=4194304
CURRENT=4194304Aborted

Any ideas? This is my first attempt at kvm so I may have missed
something. I'm using: a Core Duo cpu, kvm-16, and the Debian etch
2.6.18 kernel.

Thanks!

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Re: savevm causes 'Bus error'

[Avi Kivity]

Jon wrote:
> Hi
>
> I'd like to savevm/loadvm the state of my win2k virtual machine.
>
> This works fine with qemu or with kvm using the -no-kvm switch. But
> when kvm is enabled, issuing "savevm" causes a crash. All I get is the
> message "Bus error" on the console.
>
>   

Are you running with -std-vga?

-- 
error compiling committee.c: too many arguments to function


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Re: savevm causes 'Bus error'

[Uri Lublin]

[-- Attachment #1.1: Type: text/plain, Size: 2964 bytes --]

Hi Jon,

It seems KVM's savevm/loadvm has been broken since the upgrade to version 0.9.0 of QEMU.
Please apply the attached patch and retry.

Currently, saved images (aka snapshots) of QEMU are not compatible with those of KVM, and vice versa.
In other words if you savevm a VM started with '-no-kvm' (or a pure QEMU) you must
    start the new VM with '-no-kvm' to be able to successfully loadvm the saved image.

Regards,
    Uri

-----Original Message-----
From: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org on behalf of Jon
Sent: Thu 08/03/2007 14:31
To: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
Subject: [kvm-devel] savevm causes 'Bus error'
 
Hi

I'd like to savevm/loadvm the state of my win2k virtual machine.

This works fine with qemu or with kvm using the -no-kvm switch. But
when kvm is enabled, issuing "savevm" causes a crash. All I get is the
message "Bus error" on the console.

If I try to restore a previously saved state with kvm, I get a different crash:

qemu: warning: error while loading state for instance 0x0 of device 'ram'
unhandled vm exit:  0x80000021
rax 0000000060000010 rbx 0000000000060784 rcx 00000000000000b6 rdx
0000000000307ae3
rsi 000000000000ac2f rdi 0000000006000000 rsp 0000000000067ff6 rbp
0000000000060e14
r8  0000000000000000 r9  0000000000000000 r10 0000000000000000 r11
0000000000000000
r12 0000000000000000 r13 0000000000000000 r14 0000000000000000 r15
0000000000000000
rip 00000000000003a8 rflags 00000002
cs 0058 (00020000/0000ffff p 1 dpl 0 db 0 s 1 type a l 0 g 0 avl 0)
ds 0060 (00022ac0/0000ffff p 1 dpl 0 db 0 s 1 type 2 l 0 g 0 avl 0)
es 0060 (00022ac0/0000ffff p 1 dpl 0 db 0 s 1 type 2 l 0 g 0 avl 0)
ss 0060 (00022ac0/0000ffff p 1 dpl 0 db 0 s 1 type 2 l 0 g 0 avl 0)
fs 0060 (00022ac0/0000ffff p 1 dpl 0 db 0 s 1 type 2 l 0 g 0 avl 0)
gs 0060 (00022ac0/0000ffff p 1 dpl 0 db 0 s 1 type 2 l 0 g 0 avl 0)
tr 0028 (00023ff0/00000077 p 1 dpl 0 db 0 s 0 type 9 l 0 g 0 avl 0)
ldt 0000 (00000000/00000000 p 1 dpl 0 db 0 s 0 type 0 l 0 g 0 avl 0)
gdt 36000/3ff
idt 36400/7ff
cr0 60000010 cr2 0 cr3 30000 cr4 0 cr8 0 efer 0
cirrus_vga_load: REAL_VRAM_SIZE MISMATCH !!!!!! SAVED=4194304
CURRENT=4194304Aborted

Any ideas? This is my first attempt at kvm so I may have missed
something. I'm using: a Core Duo cpu, kvm-16, and the Debian etch
2.6.18 kernel.

Thanks!

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[-- Attachment #1.2: Type: text/html, Size: 3857 bytes --]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #2: qemu_savevm_fix.diff --]
[-- Type: text/x-patch; name="qemu_savevm_fix.diff", Size: 940 bytes --]

Index: qemu/vl.c
===================================================================
--- qemu/vl.c	(revision 4510)
+++ qemu/vl.c	(working copy)
@@ -5732,6 +5732,10 @@
     if (ram_compress_open(s, f) < 0)
         return;
     for(i = 0; i < phys_ram_size; i+= BDRV_HASH_BLOCK_SIZE) {
+#ifdef USE_KVM
+        if (kvm_allowed && (i>=0xa0000) && (i<0xc0000)) /* do not access video-addresses */
+            continue;
+#endif
 #if 0
         if (tight_savevm_enabled) {
             int64_t sector_num;
@@ -5804,6 +5808,10 @@
     if (ram_decompress_open(s, f) < 0)
         return -EINVAL;
     for(i = 0; i < phys_ram_size; i+= BDRV_HASH_BLOCK_SIZE) {
+#ifdef USE_KVM
+        if (kvm_allowed && (i>=0xa0000) && (i<0xc0000)) /* do not access video-addresses */
+            continue;
+#endif
         if (ram_decompress_buf(s, buf, 1) < 0) {
             fprintf(stderr, "Error while reading ram block header\n");
             goto error;

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Re: savevm causes 'Bus error'

[Jon]

On Thu, Mar 08, 2007 at 06:10:38AM -0800, Uri Lublin wrote:

> It seems KVM's savevm/loadvm has been broken since the upgrade to 
> version 0.9.0 of QEMU. Please apply the attached patch and retry.

Great, thanks Uri. I can now save/load with that patch applied.

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