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Subject[PATCH v6 4/4] KVM: nSVM: implement on demand allocation of the nested state
Date
This way we don't waste memory on VMs which don't use nesting
virtualization even when the host enabled it for them.

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
---
arch/x86/kvm/svm/nested.c | 42 ++++++++++++++++++++++++++++++
arch/x86/kvm/svm/svm.c | 55 ++++++++++++++++++++++-----------------
arch/x86/kvm/svm/svm.h | 6 +++++
3 files changed, 79 insertions(+), 24 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 09417f5197410..dd13856818a03 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -467,6 +467,9 @@ int nested_svm_vmrun(struct vcpu_svm *svm)

vmcb12 = map.hva;

+ if (WARN_ON(!svm->nested.initialized))
+ return 1;
+
if (!nested_vmcb_checks(svm, vmcb12)) {
vmcb12->control.exit_code = SVM_EXIT_ERR;
vmcb12->control.exit_code_hi = 0;
@@ -684,6 +687,45 @@ 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 | __GFP_ZERO);
+ if (!hsave_page)
+ return -ENOMEM;
+
+ svm->nested.hsave = page_address(hsave_page);
+
+ svm->nested.msrpm = svm_vcpu_init_msrpm();
+ if (!svm->nested.msrpm)
+ goto err_free_hsave;
+
+ svm->nested.initialized = true;
+ return 0;
+
+err_free_hsave:
+ __free_page(hsave_page);
+ return -ENOMEM;
+}
+
+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 18f8af55e970a..d1265c95e2b0b 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) {
@@ -276,9 +277,27 @@ 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 guest state, unless we are in SMM.
+ * In this case we will return to the nested guest
+ * as soon as we leave SMM.
+ */
+ if (!is_smm(&svm->vcpu))
+ svm_free_nested(svm);
+
+ } else {
+ int ret = svm_allocate_nested(svm);
+
+ if (ret) {
+ vcpu->arch.efer = old_efer;
+ return ret;
+ }
+ }
}

svm->vmcb->save.efer = efer | EFER_SVME;
@@ -610,7 +629,7 @@ static void set_msr_interception(u32 *msrpm, unsigned msr,
msrpm[offset] = tmp;
}

-static u32 *svm_vcpu_init_msrpm(void)
+u32 *svm_vcpu_init_msrpm(void)
{
int i;
u32 *msrpm;
@@ -630,7 +649,7 @@ static u32 *svm_vcpu_init_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);
}
@@ -1204,7 +1223,6 @@ 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);
@@ -1215,13 +1233,9 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)
if (!vmcb_page)
goto out;

- hsave_page = alloc_page(GFP_KERNEL_ACCOUNT | __GFP_ZERO);
- if (!hsave_page)
- goto error_free_vmcb_page;
-
err = avic_init_vcpu(svm);
if (err)
- goto error_free_hsave_page;
+ 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.
@@ -1229,15 +1243,9 @@ 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);
-
svm->msrpm = svm_vcpu_init_msrpm();
if (!svm->msrpm)
- goto error_free_hsave_page;
-
- svm->nested.msrpm = svm_vcpu_init_msrpm();
- if (!svm->nested.msrpm)
- goto error_free_msrpm;
+ goto error_free_vmcb_page;

svm->vmcb = page_address(vmcb_page);
svm->vmcb_pa = __sme_set(page_to_pfn(vmcb_page) << PAGE_SHIFT);
@@ -1249,10 +1257,6 @@ static int svm_create_vcpu(struct kvm_vcpu *vcpu)

return 0;

-error_free_msrpm:
- svm_vcpu_free_msrpm(svm->msrpm);
-error_free_hsave_page:
- __free_page(hsave_page);
error_free_vmcb_page:
__free_page(vmcb_page);
out:
@@ -1278,10 +1282,10 @@ 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)
@@ -3964,6 +3968,9 @@ static int svm_pre_leave_smm(struct kvm_vcpu *vcpu, const char *smstate)
gpa_to_gfn(vmcb12_gpa), &map) == -EINVAL)
return 1;

+ if (svm_allocate_nested(svm))
+ return 1;
+
ret = enter_svm_guest_mode(svm, vmcb12_gpa, map.hva);
kvm_vcpu_unmap(&svm->vcpu, &map, true);
}
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 1e1842de0efe7..10453abc5bed3 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -96,6 +96,8 @@ struct svm_nested_state {

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

struct vcpu_svm {
@@ -339,6 +341,8 @@ static inline bool gif_set(struct vcpu_svm *svm)

u32 svm_msrpm_offset(u32 msr);
int svm_set_efer(struct kvm_vcpu *vcpu, u64 efer);
+u32 *svm_vcpu_init_msrpm(void);
+void svm_vcpu_free_msrpm(u32 *msrpm);
void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0);
int svm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4);
void svm_flush_tlb(struct kvm_vcpu *vcpu);
@@ -379,6 +383,8 @@ 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
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