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>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 2e8729678600aa95a551a60a1f1661e1fa065520..ae22dcf172112584661ebd2620eb76305cbf5148 100644 (file)
--- 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);