[PATCH 5/8] KVM: nSVM: implement ondemand allocation of the nested state

Maxim Levitsky
2020-08-20T09:15:55Z

This way we don't waste memory on VMs which don't enable
nesting virtualization

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/kvm/svm/nested.c | 43 +++++++++++++++++++++++++++
arch/x86/kvm/svm/svm.c | 62 +++++++++++++++++++++++----------------
arch/x86/kvm/svm/svm.h | 6 ++++
3 files changed, 85 insertions(+), 26 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index d9755eab2199..b6704611fc02 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -473,6 +473,9 @@ int nested_svm_vmrun(struct vcpu_svm *svm)

nested_vmcb = map.hva;

+ if (WARN_ON(!svm->nested.initialized))
+ return 1;
+
if (!nested_vmcb_checks(svm, nested_vmcb)) {
nested_vmcb->control.exit_code = SVM_EXIT_ERR;
nested_vmcb->control.exit_code_hi = 0;
@@ -686,6 +689,46 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
return 0;
}

+int svm_allocate_nested(struct vcpu_svm *svm)
+{
+ struct page *hsave_page;
+
+ if (svm->nested.initialized)
+ return 0;
+
+ hsave_page = alloc_page(GFP_KERNEL_ACCOUNT);
+ if (!hsave_page)
+ goto free_page1;
+
+ svm->nested.hsave = page_address(hsave_page);
+ clear_page(svm->nested.hsave);
+
+ svm->nested.msrpm = svm_vcpu_alloc_msrpm();
+ if (!svm->nested.msrpm)
+ goto free_page2;
+
+ svm->nested.initialized = true;
+ return 0;
+free_page2:
+ __free_page(hsave_page);
+free_page1:
+ return 1;
+}
+
+void svm_free_nested(struct vcpu_svm *svm)
+{
+ if (!svm->nested.initialized)
+ return;
+
+ svm_vcpu_free_msrpm(svm->nested.msrpm);
+ svm->nested.msrpm = NULL;
+
+ __free_page(virt_to_page(svm->nested.hsave));
+ svm->nested.hsave = NULL;
+
+ svm->nested.initialized = false;
+}
+
/*
* Forcibly leave nested mode in order to be able to reset the VCPU later on.
*/
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index ce0773c9a7fa..d941acc36b50 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -266,6 +266,7 @@ static int get_max_npt_level(void)
int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
{
struct vcpu_svm *svm = to_svm(vcpu);
+ u64 old_efer = vcpu->arch.efer;
vcpu->arch.efer = efer;

if (!npt_enabled) {
@@ -276,14 +277,31 @@ int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer)
efer &= ~EFER_LME;
}

- if (!(efer & EFER_SVME)) {
- svm_leave_nested(svm);
- svm_set_gif(svm, true);
+ if ((old_efer & EFER_SVME) != (efer & EFER_SVME)) {
+ if (!(efer & EFER_SVME)) {
+ svm_leave_nested(svm);
+ svm_set_gif(svm, true);
+
+ /*
+ * Free the nested state unless we are in SMM, in which
+ * case the exit from SVM mode is only for duration of the SMI
+ * handler
+ */
+ if (!is_smm(&svm->vcpu))
+ svm_free_nested(svm);
+
+ } else {
+ if (svm_allocate_nested(svm))
+ goto error;
+ }
}

svm->vmcb->save.efer = efer | EFER_SVME;
vmcb_mark_dirty(svm->vmcb, VMCB_CR);
return 0;
+error:
+ vcpu->arch.efer = old_efer;
+ return 1;
}

static int is_external_interrupt(u32 info)
@@ -610,7 +628,7 @@ static void set_msr_interception(u32 *msrpm, unsigned msr,
msrpm[offset] = tmp;
}

-static u32 *svm_vcpu_alloc_msrpm(void)
+u32 *svm_vcpu_alloc_msrpm(void)
{
int i;
u32 *msrpm;
@@ -630,7 +648,7 @@ static u32 *svm_vcpu_alloc_msrpm(void)
return msrpm;
}

-static void svm_vcpu_free_msrpm(u32 *msrpm)
+void svm_vcpu_free_msrpm(u32 *msrpm)
{
__free_pages(virt_to_page(msrpm), MSRPM_ALLOC_ORDER);
}
@@ -1184,7 +1202,6 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm;
struct page *vmcb_page;
- struct page *hsave_page;
int err;

BUILD_BUG_ON(offsetof(struct vcpu_svm, vcpu) != 0);
@@ -1195,13 +1212,9 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
if (!vmcb_page)
goto out;

- hsave_page = alloc_page(GFP_KERNEL_ACCOUNT);
- if (!hsave_page)
- goto free_page1;
-
err = avic_init_vcpu(svm);
if (err)
- goto free_page2;
+ goto out;

/* We initialize this flag to true to make sure that the is_running
* bit would be set the first time the vcpu is loaded.
@@ -1209,16 +1222,9 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
if (irqchip_in_kernel(vcpu->kvm) && kvm_apicv_activated(vcpu->kvm))
svm->avic_is_running = true;

- svm->nested.hsave = page_address(hsave_page);
- clear_page(svm->nested.hsave);
-
svm->msrpm = svm_vcpu_alloc_msrpm();
if (!svm->msrpm)
- goto free_page2;
-
- svm->nested.msrpm = svm_vcpu_alloc_msrpm();
- if (!svm->nested.msrpm)
- goto free_page3;
+ goto free_page;

svm->vmcb = page_address(vmcb_page);
clear_page(svm->vmcb);
@@ -1231,11 +1237,7 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)

return 0;

-free_page3:
- svm_vcpu_free_msrpm(svm->msrpm);
-free_page2:
- __free_page(hsave_page);
-free_page1:
+free_page:
__free_page(vmcb_page);
out:
return err;
@@ -1260,10 +1262,10 @@ static void svm_free_vcpu(struct kvm_vcpu *vcpu)
*/
svm_clear_current_vmcb(svm->vmcb);

+ svm_free_nested(svm);
+
__free_page(pfn_to_page(__sme_clr(svm->vmcb_pa) >> PAGE_SHIFT));
__free_pages(virt_to_page(svm->msrpm), MSRPM_ALLOC_ORDER);
- __free_page(virt_to_page(svm->nested.hsave));
- __free_pages(virt_to_page(svm->nested.msrpm), MSRPM_ALLOC_ORDER);
}

static void svm_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
@@ -3912,6 +3914,14 @@ static int svm_pre_leave_smm(struct kvm_vcpu *vcpu, const char *smstate)
vmcb_gpa = GET_SMSTATE(u64, smstate, 0x7ee0);

if (guest) {
+ /*
+ * This can happen if SVM was not enabled prior to #SMI,
+ * but guest corrupted the #SMI state and marked it as
+ * enabled it there
+ */
+ if (!svm->nested.initialized)
+ return 1;
+
if (kvm_vcpu_map(&svm->vcpu, gpa_to_gfn(vmcb_gpa), &map) == -EINVAL)
return 1;

diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index ef16f708ed1c..9dca64a2edb5 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -97,6 +97,8 @@ struct svm_nested_state {

/* cache for control fields of the guest */
struct vmcb_control_area ctl;
+
+ bool initialized;
};

struct vcpu_svm {
@@ -349,6 +351,8 @@ static inline bool gif_set(struct vcpu_svm *svm)
#define MSR_INVALID 0xffffffffU

u32 svm_msrpm_offset(u32 msr);
+u32 *svm_vcpu_alloc_msrpm(void);
+void svm_vcpu_free_msrpm(u32 *msrpm);
int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer);
void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
int svm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
@@ -390,6 +394,8 @@ static inline bool nested_exit_on_nmi(struct vcpu_svm *svm)
int enter_svm_guest_mode(struct vcpu_svm *svm, u64 vmcb_gpa,
struct vmcb *nested_vmcb);
void svm_leave_nested(struct vcpu_svm *svm);
+void svm_free_nested(struct vcpu_svm *svm);
+int svm_allocate_nested(struct vcpu_svm *svm);
int nested_svm_vmrun(struct vcpu_svm *svm);
void nested_svm_vmloadsave(struct vmcb *from_vmcb, struct vmcb *to_vmcb);
int nested_svm_vmexit(struct vcpu_svm *svm);
--
2.26.2