>>> Ian Campbell <ian.campb...@citrix.com> 23.11.09 17:44 >>> >On Mon, 2009-11-23 at 16:31 +0000, Jan Beulich wrote: >> >> It does not happen on XenSource 2.6.18 kernel >> > >> >I assume that this kernel (perhaps coincidentally) manages to use >> >FLAT_USER_CS32 for compat mode processes. >> > >> >> , or the Debian 2.6.26 kernel. >> > >> >This was a forward ported 2.6.18-style kernel so I guess the same reason >> >as 2.6.18. >> >> If your analysis was right, 2.6.18 as well as our forward ported kernels >> should also be affected (both ia32_sysenter_target and ia32_cstar_target >> store __USER32_CS to the frame, and return via HYPERVISOR_iret), yet >> supposedly they don't have the problem (though I can't say why that >> would be). So perhaps there's some other yet un-described aspect to >> this, or I'm being confused by something... > >I didn't try any of these kernels myself so I don't really know what >happens.
Okay, I think I spotted the relevant difference: 2.6.18 and forward ports set VGCF_in_syscall only when returning from 64-bit system calls (through ret_from_sys_call) - 32-bit syscalls (regardless of the entry path taken) return through int_ret_from_sys_call. 32-bit guest kernels shouldn't be affected by this, as compat mode returns from the hypervisor (compat_restore_all_guest) always use iret. Jan -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
