On Tue, Nov 20, 2018 at 8:03 AM, Liran Alon <liran.alon@xxxxxxxxxx> wrote:
> When guest transitions from/to long-mode by modifying MSR_EFER.LMA,
> the list of shared MSRs to be saved/restored on guest<->host
> transitions is updated (See vmx_set_efer() call to setup_msrs()).
>
> On every entry to guest, vcpu_enter_guest() calls
> vmx_prepare_switch_to_guest(). This function should also take care
> of setting the shared MSRs to be saved/restored. However, the
> function does nothing in case we are already running with loaded
> guest state (vmx->loaded_cpu_state != NULL).
>
> This means that even when guest modifies MSR_EFER.LMA which results
> in updating the list of shared MSRs, it isn't being taken into account
> by vmx_prepare_switch_to_guest() because it happens while we are
> running with loaded guest state.
>
> To fix above mentioned issue, add a flag to mark that the list of
> shared MSRs has been updated and modify vmx_prepare_switch_to_guest()
> to set shared MSRs when running with host state *OR* list of shared
> MSRs has been updated.
>
> Note that this issue was mistakenly introduced by commit
> 678e315e78a7 ("KVM: vmx: add dedicated utility to access guest's
> kernel_gs_base") because previously vmx_set_efer() always called
> vmx_load_host_state() which resulted in vmx_prepare_switch_to_guest() to
> set shared MSRs.
>
> Fixes: 678e315e78a7 ("KVM: vmx: add dedicated utility to access guest's kernel_gs_base")
>
> Reported-by: Eyal Moscovici <eyal.moscovici@xxxxxxxxxx>
> Reviewed-by: Mihai Carabas <mihai.carabas@xxxxxxxxxx>
> Reviewed-by: Liam Merwick <liam.merwick@xxxxxxxxxx>
> Signed-off-by: Liran Alon <liran.alon@xxxxxxxxxx>
Reviewed-by: Jim Mattson <jmattson@xxxxxxxxxx>
