Ingo Molnar wrote:
> hm, i just noticed that in vmx_vcpu_run() KVM restores %fs quite late.
>
> This is a bit awkward under v2.6.21 x86 because there we use %fs for the
> KERNEL_PDA area. Things like 'current' rely on it. So maybe we should
> just do this unconditionally in assembly:
>
> movl $(__KERNEL_PDA), %edx;
> movl %edx, %fs
>
Sure, but with %dx instead of %edx, please.
> it's also a problem with -rt too, which has that whole codepath up to
> the load_fs() call preemptible.
>
> 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.
Non -rt kvm cannot preempt there even with CONFIG_PREEMPT=y. Can
interrupts reference current? If so, that fix is needed badly for .21.
--
error compiling committee.c: too many arguments to function
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