Xen, Xorg and radeon trying to create a new domU instance

I got signal 11 from X when I try to start a new domU instance.

I have no problem as long as I do not start a new instance.
Backtrace:
485.022] 0: /usr/bin/Xorg (xorg_backtrace+0x28) [0x48daf8]
485.022] 1: /usr/bin/Xorg (0x400000+0x6ae89) [0x46ae89]
485.022] 2: /lib64/libc.so.6 (0x7f096a465000+0x32a60) [0x7f096a497a60]
485.022] 3: /lib64/libc.so.6 (memcpy+0xd2) [0x7f096a4e48e2]
485.022] 4: /usr/lib64/xorg/modules/drivers/radeon_drv.so (0x7f096833b000+0x
c194b) [0x7f09683fc94b]
485.022] 5: /usr/lib64/xorg/modules/libexa.so (0x7f09676eb000+0x947f) [0x7f0
9676f447f]
485.022] 6: /usr/lib64/xorg/modules/libexa.so (0x7f09676eb000+0x95ad) [0x7f0
9676f45ad]
485.022] 7: /usr/bin/Xorg (miCopyRegion+0x13d) [0x530d3d]
485.022] 8: /usr/bin/Xorg (miDoCopy+0x461) [0x5313c1]
485.022] 9: /usr/lib64/xorg/modules/libexa.so (0x7f09676eb000+0x8577) [0x7f0
9676f3577]
485.022] 10: /usr/bin/Xorg (0x400000+0xb357d) [0x4b357d]
485.022] 11: /usr/bin/Xorg (0x400000+0x141760) [0x541760]
485.022] 12: /usr/bin/Xorg (0x400000+0x1732d9) [0x5732d9]
485.023] 13: /usr/bin/Xorg (0x400000+0x17467d) [0x57467d]
485.023] 14: /usr/bin/Xorg (0x400000+0xb06dc) [0x4b06dc]
485.023] 15: /usr/bin/Xorg (0x400000+0xb0a76) [0x4b0a76]
485.023] 16: /usr/bin/Xorg (0x400000+0xb0ba8) [0x4b0ba8]
485.023] 17: /usr/bin/Xorg (0x400000+0xb1dff) [0x4b1dff]
485.023] 18: /usr/bin/Xorg (miPaintWindow+0x1ab) [0x45d37b]
485.023] 19: /usr/bin/Xorg (miWindowExposures+0xc2) [0x45d532]
485.023] 20: /usr/bin/Xorg (0x400000+0x107027) [0x507027]
485.023] 21: /usr/bin/Xorg (miHandleValidateExposures+0x2b) [0x52399b]
485.023] 22: /usr/bin/Xorg (0x400000+0xf328f) [0x4f328f]
485.023] 23: /usr/lib64/xorg/modules/libexa.so (0x7f09676eb000+0x281f) [0x7f
09676ed81f]
485.023] 24: /usr/bin/Xorg (0x400000+0x11d490) [0x51d490]
485.023] 25: /usr/bin/Xorg (xf86Wakeup+0x54d) [0x47a6ed]
485.023] 26: /usr/bin/Xorg (WakeupHandler+0x4b) [0x4416ab]
485.023] 27: /usr/bin/Xorg (WaitForSomething+0x1ca) [0x46bb3a]
485.023] 28: /usr/bin/Xorg (0x400000+0x409b2) [0x4409b2]
485.023] 29: /usr/bin/Xorg (0x400000+0x25f3a) [0x425f3a]
485.023] 30: /lib64/libc.so.6 (__libc_start_main+0xfd) [0x7f096a483b7d]
485.023] 31: /usr/bin/Xorg (0x400000+0x25af9) [0x425af9]
485.023] Segmentation fault at address (nil)
485.023]
Fatal server error:
485.023] Caught signal 11 (Segmentation fault). Server aborting
485.023]

I found the answer. Disable KMS and the problem is gone until the next version of xen 4.0.1 may fix it.