[PATCH AUTOSEL 4.19 080/123] KVM: VMX: Update shared MSRs to be saved/restored on MSR_EFER.LMA changes

Sasha Levin
2018-12-05T09:40:33Z

From: Liran Alon <liran.alon@oracle.com>

[ Upstream commit f48b4711dd6e1cf282f9dfd159c14a305909c97c ]

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@oracle.com>
Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Liam Merwick <liam.merwick@oracle.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 9f3def7baa6d..bdd46628c107 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -961,6 +961,7 @@ 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;
@@ -2873,6 +2874,20 @@ 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;

@@ -2933,11 +2948,6 @@ 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)
@@ -3417,6 +3427,7 @@ 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);
--
2.17.1