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>
---
arch/x86/kvm/vmx.c | 21 ++++++++++++++++-----
1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 4555077d69ce..aa6afbd20c08 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -984,6 +984,7 @@ struct vcpu_vmx {
struct shared_msr_entry *guest_msrs;
int nmsrs;
int save_nmsrs;
+ bool guest_msrs_dirty;
unsigned long host_idt_base;
#ifdef CONFIG_X86_64
u64 msr_host_kernel_gs_base;
@@ -2897,6 +2898,20 @@ static void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
vmx->req_immediate_exit = false;
+ /*
+ * Note that guest MSRs to be saved/restored can also be changed
+ * when guest state is loaded. This happens when guest transitions
+ * to/from long-mode by setting MSR_EFER.LMA.
+ */
+ if (!vmx->loaded_cpu_state || vmx->guest_msrs_dirty) {
+ vmx->guest_msrs_dirty = false;
+ for (i = 0; i < vmx->save_nmsrs; ++i)
+ kvm_set_shared_msr(vmx->guest_msrs[i].index,
+ vmx->guest_msrs[i].data,
+ vmx->guest_msrs[i].mask);
+
+ }
+
if (vmx->loaded_cpu_state)
return;
@@ -2957,11 +2972,6 @@ static void vmx_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
vmcs_writel(HOST_GS_BASE, gs_base);
host_state->gs_base = gs_base;
}
-
- for (i = 0; i < vmx->save_nmsrs; ++i)
- kvm_set_shared_msr(vmx->guest_msrs[i].index,
- vmx->guest_msrs[i].data,
- vmx->guest_msrs[i].mask);
}
static void vmx_prepare_switch_to_host(struct vcpu_vmx *vmx)
@@ -3436,6 +3446,7 @@ static void setup_msrs(struct vcpu_vmx *vmx)
move_msr_up(vmx, index, save_nmsrs++);
vmx->save_nmsrs = save_nmsrs;
+ vmx->guest_msrs_dirty = true;
if (cpu_has_vmx_msr_bitmap())
vmx_update_msr_bitmap(&vmx->vcpu);
--
2.16.1
