KVM: VMX: Add facility to atomically switch MSRs on guest entry/exit

Some guest msr values cannot be used on the host (for example. EFER.NX=0),
so we need to switch them atomically during guest entry or exit.

Add a facility to program the vmx msr autoload registers accordingly.

Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 49 insertions, 0 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 2e872967860..ae22dcf1721 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -98,6 +98,8 @@ module_param(ple_gap, int, S_IRUGO);
 static int ple_window = KVM_VMX_DEFAULT_PLE_WINDOW;
 module_param(ple_window, int, S_IRUGO);
 
+#define NR_AUTOLOAD_MSRS 1
+
 struct vmcs {
         u32 revision_id;
         u32 abort;
@@ -125,6 +127,11 @@ struct vcpu_vmx {
         u64                   msr_guest_kernel_gs_base;
 #endif
         struct vmcs          *vmcs;
+        struct msr_autoload {
+                unsigned nr;
+                struct vmx_msr_entry guest[NR_AUTOLOAD_MSRS];
+                struct vmx_msr_entry host[NR_AUTOLOAD_MSRS];
+        } msr_autoload;
         struct {
                 int           loaded;
                 u16           fs_sel, gs_sel, ldt_sel;
@@ -595,6 +602,46 @@ static void update_exception_bitmap(struct kvm_vcpu *vcpu)
         vmcs_write32(EXCEPTION_BITMAP, eb);
 }
 
+static void clear_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr)
+{
+        unsigned i;
+        struct msr_autoload *m = &vmx->msr_autoload;
+
+        for (i = 0; i < m->nr; ++i)
+                if (m->guest[i].index == msr)
+                        break;
+
+        if (i == m->nr)
+                return;
+        --m->nr;
+        m->guest[i] = m->guest[m->nr];
+        m->host[i] = m->host[m->nr];
+        vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, m->nr);
+        vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, m->nr);
+}
+
+static void add_atomic_switch_msr(struct vcpu_vmx *vmx, unsigned msr,
+                                  u64 guest_val, u64 host_val)
+{
+        unsigned i;
+        struct msr_autoload *m = &vmx->msr_autoload;
+
+        for (i = 0; i < m->nr; ++i)
+                if (m->guest[i].index == msr)
+                        break;
+
+        if (i == m->nr) {
+                ++m->nr;
+                vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, m->nr);
+                vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, m->nr);
+        }
+
+        m->guest[i].index = msr;
+        m->guest[i].value = guest_val;
+        m->host[i].index = msr;
+        m->host[i].value = host_val;
+}
+
 static void reload_tss(void)
 {
         /*
@@ -2470,7 +2517,9 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
         vmcs_writel(HOST_RIP, kvm_vmx_return); /* 22.2.5 */
         vmcs_write32(VM_EXIT_MSR_STORE_COUNT, 0);
         vmcs_write32(VM_EXIT_MSR_LOAD_COUNT, 0);
+        vmcs_write64(VM_EXIT_MSR_LOAD_ADDR, __pa(vmx->msr_autoload.host));
         vmcs_write32(VM_ENTRY_MSR_LOAD_COUNT, 0);
+        vmcs_write64(VM_ENTRY_MSR_LOAD_ADDR, __pa(vmx->msr_autoload.guest));
 
         rdmsr(MSR_IA32_SYSENTER_CS, host_sysenter_cs, junk);
         vmcs_write32(HOST_IA32_SYSENTER_CS, host_sysenter_cs);