On Tue, Jul 31, 2012 at 12:11:13PM +0300, Avi Kivity wrote:
> On 07/31/2012 02:36 AM, Marcelo Tosatti wrote:
> > On Mon, Jul 30, 2012 at 07:39:31PM +0300, Avi Kivity wrote:
> >> On 07/30/2012 05:07 PM, Chris Clayton wrote:
> >> >>
> >> >>>> With kernel 3.5.0 with b2da15ac26a0c00 reverted, I have just had 15
> >> >>>> clean invocations of vanilla qemu-kvm-1.1.1. So that commit would seem
> >> >>>> to be the problem.
> >> >>>
> >> >>> Just to be sure, I've run some more tests today. No crashes occurred in
> >> >>> 20 runs of vanilla qemu-kvm-1.1.1 on kernel 3.5.0 with b2da15ac26a0c00
> >> >>> reverted.
> >> >>
> >> >> Ok. I'm trying to reproduce it here on a nested-virt setup, since the
> >> >> code looks correct.
> >> >>
> >> >> What's your preemption settings?
> >> >>
> >> >>
> >> > [chris:~/kernel/linux-3.5.0]$ grep PREEMPT .config
> >> > CONFIG_TREE_PREEMPT_RCU=y
> >> > CONFIG_PREEMPT_RCU=y
> >> > CONFIG_PREEMPT_NOTIFIERS=y
> >> > # CONFIG_PREEMPT_NONE is not set
> >> > # CONFIG_PREEMPT_VOLUNTARY is not set
> >> > CONFIG_PREEMPT=y
> >> > CONFIG_PREEMPT_COUNT=y
> >>
> >> Here's what I think that is happening
> >>
> >> vcpu_load
> >> ...
> >> vmx_save_host_state
> >> vmx_vcpu_run
> >> (ds.cpl, es.cpl cleared by hardware)
> >>
> >> interrupt
> >> push ds, es # pushes bad ds, es
> >> schedule
> >> vmx_vcpu_put
> >> vmx_load_host_state
> >> reload ds, es
> >> pop ds, es # of other thread's stack
> >> iret
> >> # other thread runs
> >> interrupt
> >> schedule # back in vcpu thread
> >> interrupt return: pop ds, es # <-- problem
> >> iret
> >>
> >> ...
> >> vcpu_put
> >>
> >> # bad ds, es, but !vmx->host_state.loaded
> >>
> >> Marcelo, did I miss something here?
> >
> > Don't think so.
>
> So the same problem should happen with %fs and %gs, no?
AFAICS:
depends on CONFIG_X86_32_LAZY_GS for GS, unconditional for FS.
> x86_64 is safe, since it entry_64.S never saves/restores segment registers.
Is the comment
/*
* The sysexit path does not restore ds/es, so we must set them
* to
* a reasonable value ourselves.
*/
Correct?
syscall_exit -> syscall_exit_work -> resume_userspace ->
restore_all -> RESTORE_REGS
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