Re: %fs PDA & KVM

[Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>]

* Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org> wrote:

> >i'm also wondering about this bit:
> >
> >        kvm_run->exit_type = 0;
> >        if (fail) {
> >                kvm_run->exit_type = KVM_EXIT_TYPE_FAIL_ENTRY;
> >                kvm_run->exit_reason = vmcs_read32(VM_INSTRUCTION_ERROR);
> >                kvm_cr3_cache_sync(vcpu);
> >                r = 0;
> >        } else {
> >                if (fs_gs_ldt_reload_needed) {
> >                        load_ldt(ldt_sel);
> >                        load_fs(fs_sel);
> >
> >are you sure we dont need an FS reload in the 'fail' case?
> >  
> 
> The manual is not explicit about it, but I think that an entry failure 
> during loading of guest state _can_ cause fs to be loaded, so yes, 
> that path is missing the segment reloads.

ok, i'll send a patch.

> Non -rt kvm cannot preempt there even with CONFIG_PREEMPT=y.  Can 
> interrupts reference current?  If so, that fix is needed badly for 
> .21.

interrupts can reference 'current' (although it's generally not 
encouraged) - for example scheduler_tick(), but the IRQ entry code loads 
%fs anyway via SAVE_ALL, so it's not an issue.

	Ingo

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