> On 20 Nov 2018, at 20:20, Jim Mattson <jmattson@xxxxxxxxxx> wrote:
>
> 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>
Paolo, I saw this patch don’t have a Cc to stable tree. It seems that it should have one as-well as it also fixes an important regression issue.
-Liran
