[RFC PATCH 2/3] nSVM: introduce smv->nested.save to cache save area fields

[Emanuele Giuseppe Esposito]

This is useful in next patch, to avoid having temporary
copies of vmcb12 registers and passing them manually.

Right now, instead of blindly copying everything,
we just copy EFER, CR0, CR3, CR4, DR6 and DR7. If more fields
will need to be added, it will be more obvious to see
that they must be added in copy_vmcb_save_area,
otherwise the checks will fail.

Signed-off-by: Emanuele Giuseppe Esposito <eesposit@xxxxxxxxxx>
---
 arch/x86/kvm/svm/nested.c | 24 ++++++++++++++++++++++++
 arch/x86/kvm/svm/svm.c    |  1 +
 arch/x86/kvm/svm/svm.h    |  3 +++
 3 files changed, 28 insertions(+)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index d2fe65e2a7a4..2491c77203c7 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -194,6 +194,22 @@ static void copy_vmcb_control_area(struct vmcb_control_area *dst,
 	dst->pause_filter_thresh  = from->pause_filter_thresh;
 }
 
+static void copy_vmcb_save_area(struct vmcb_save_area *dst,
+				struct vmcb_save_area *from)
+{
+	/*
+	 * Copy only necessary fields, as we need them
+	 * to avoid TOC/TOU races.
+	 */
+	dst->efer = from->efer;
+	dst->cr0 = from->cr0;
+	dst->cr3 = from->cr3;
+	dst->cr4 = from->cr4;
+
+	dst->dr6 = from->dr6;
+	dst->dr7 = from->dr7;
+}
+
 static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)
 {
 	/*
@@ -313,6 +329,12 @@ void nested_load_control_from_vmcb12(struct vcpu_svm *svm,
 	svm->nested.ctl.iopm_base_pa  &= ~0x0fffULL;
 }
 
+void nested_load_save_from_vmcb12(struct vcpu_svm *svm,
+				  struct vmcb_save_area *save)
+{
+	copy_vmcb_save_area(&svm->nested.save, save);
+}
+
 /*
  * Synchronize fields that are written by the processor, so that
  * they can be copied back into the vmcb12.
@@ -647,6 +669,7 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
 		return -EINVAL;
 
 	nested_load_control_from_vmcb12(svm, &vmcb12->control);
+	nested_load_save_from_vmcb12(svm, &vmcb12->save);
 
 	if (!nested_vmcb_valid_sregs(vcpu, &vmcb12->save) ||
 	    !nested_vmcb_check_controls(vcpu, &svm->nested.ctl)) {
@@ -1385,6 +1408,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
 
 	svm_copy_vmrun_state(&svm->vmcb01.ptr->save, save);
 	nested_load_control_from_vmcb12(svm, ctl);
+	nested_load_save_from_vmcb12(svm, save);
 
 	svm_switch_vmcb(svm, &svm->nested.vmcb02);
 	nested_vmcb02_prepare_control(svm);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 69639f9624f5..169b930322ef 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -4386,6 +4386,7 @@ static int svm_leave_smm(struct kvm_vcpu *vcpu, const char *smstate)
 			vmcb12 = map.hva;
 
 			nested_load_control_from_vmcb12(svm, &vmcb12->control);
+			nested_load_save_from_vmcb12(svm, &vmcb12->save);
 
 			ret = enter_svm_guest_mode(vcpu, vmcb12_gpa, vmcb12);
 			kvm_vcpu_unmap(vcpu, &map, true);
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index bd0fe94c2920..6d12814cf64c 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -119,6 +119,7 @@ struct svm_nested_state {
 
 	/* cache for control fields of the guest */
 	struct vmcb_control_area ctl;
+	struct vmcb_save_area save;
 
 	bool initialized;
 };
@@ -484,6 +485,8 @@ int nested_svm_check_exception(struct vcpu_svm *svm, unsigned nr,
 int nested_svm_exit_special(struct vcpu_svm *svm);
 void nested_load_control_from_vmcb12(struct vcpu_svm *svm,
 				     struct vmcb_control_area *control);
+void nested_load_save_from_vmcb12(struct vcpu_svm *svm,
+				  struct vmcb_save_area *save);
 void nested_sync_control_from_vmcb02(struct vcpu_svm *svm);
 void nested_vmcb02_compute_g_pat(struct vcpu_svm *svm);
 void svm_switch_vmcb(struct vcpu_svm *svm, struct kvm_vmcb_info *target_vmcb);
-- 
2.27.0