[PATCH 5/5] KVM: nSVM: Implement Enlightened MSR-Bitmap feature

Vitaly Kuznetsov
2021-12-20T15:23:06Z

Similar to nVMX commit 502d2bf5f2fd ("KVM: nVMX: Implement Enlightened MSR
Bitmap feature"), add support for the feature for nSVM (Hyper-V on KVM).

Notable differences from nVMX implementation:
- As the feature uses SW reserved fields in VMCB control, KVM needs to
make sure it's dealing with a Hyper-V guest (kvm_hv_hypercall_enabled()).

- 'msrpm_base_pa' needs to be always be overwritten in
nested_svm_vmrun_msrpm(), even when the update is skipped. As an
optimization, nested_vmcb02_prepare_control() copies it from VMCB01
so when MSR-Bitmap feature for L2 is disabled nothing needs to be done.

- 'struct vmcb_ctrl_area_cached' needs to be extended with clean
fields/sw reserved data and __nested_copy_vmcb_control_to_cache() needs to
copy it so nested_svm_vmrun_msrpm() can use it later.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/kvm/hyperv.c | 7 +------
arch/x86/kvm/svm/nested.c | 41 ++++++++++++++++++++++++++++++++-------
arch/x86/kvm/svm/svm.h | 2 ++
3 files changed, 37 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index c008522112f6..18af9e67be40 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2409,10 +2409,6 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
if (kvm_x86_ops.nested_ops->get_evmcs_version)
evmcs_ver = kvm_x86_ops.nested_ops->get_evmcs_version(vcpu);

- /* Skip NESTED_FEATURES if eVMCS is not supported */
- if (!evmcs_ver)
- --nent;
-
if (cpuid->nent < nent)
return -E2BIG;

@@ -2512,8 +2508,7 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,

case HYPERV_CPUID_NESTED_FEATURES:
ent->eax = evmcs_ver;
- if (evmcs_ver)
- ent->eax |= HV_X64_NESTED_MSR_BITMAP;
+ ent->eax |= HV_X64_NESTED_MSR_BITMAP;

break;

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index f27323728be2..c975570188e9 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -28,6 +28,7 @@
#include "cpuid.h"
#include "lapic.h"
#include "svm.h"
+#include "svm_onhyperv.h"

#define CC KVM_NESTED_VMENTER_CONSISTENCY_CHECK

@@ -165,14 +166,30 @@ void recalc_intercepts(struct vcpu_svm *svm)
vmcb_set_intercept(c, INTERCEPT_VMSAVE);
}

+/*
+ * Merge L0's (KVM) and L1's (Nested VMCB) MSR permission bitmaps. The function
+ * is optimized in that it only merges the parts where KVM MSR permission bitmap
+ * may contain zero bits.
+ */
static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)
{
+ struct hv_enlightenments *hve =
+ (struct hv_enlightenments *)svm->nested.ctl.reserved_sw;
+ int i;
+
/*
- * This function merges the msr permission bitmaps of kvm and the
- * nested vmcb. It is optimized in that it only merges the parts where
- * the kvm msr permission bitmap may contain zero bits
+ * MSR bitmap update can be skipped when:
+ * - MSR bitmap for L1 hasn't changed.
+ * - Nested hypervisor (L1) is attempting to launch the same L2 as
+ * before.
+ * - Nested hypervisor (L1) is using Hyper-V emulation interface and
+ * tells KVM (L0) there were no changes in MSR bitmap for L2.
*/
- int i;
+ if (!svm->nested.force_msr_bitmap_recalc &&
+ kvm_hv_hypercall_enabled(&svm->vcpu) &&
+ hve->hv_enlightenments_control.msr_bitmap &&
+ (svm->nested.ctl.clean & VMCB_HV_NESTED_ENLIGHTENMENTS))
+ goto set_msrpm_base_pa;

if (!(vmcb12_is_intercept(&svm->nested.ctl, INTERCEPT_MSR_PROT)))
return true;
@@ -195,6 +212,7 @@ static bool nested_svm_vmrun_msrpm(struct vcpu_svm *svm)

svm->nested.force_msr_bitmap_recalc = false;

+set_msrpm_base_pa:
svm->vmcb->control.msrpm_base_pa = __sme_set(__pa(svm->nested.msrpm));

return true;
@@ -300,7 +318,8 @@ static bool nested_vmcb_check_controls(struct kvm_vcpu *vcpu)
}

static
-void __nested_copy_vmcb_control_to_cache(struct vmcb_ctrl_area_cached *to,
+void __nested_copy_vmcb_control_to_cache(struct kvm_vcpu *vcpu,
+ struct vmcb_ctrl_area_cached *to,
struct vmcb_control_area *from)
{
unsigned int i;
@@ -333,12 +352,19 @@ void __nested_copy_vmcb_control_to_cache(struct vmcb_ctrl_area_cached *to,
to->asid = from->asid;
to->msrpm_base_pa &= ~0x0fffULL;
to->iopm_base_pa &= ~0x0fffULL;
+
+ /* Hyper-V extensions (Enlightened VMCB) */
+ if (kvm_hv_hypercall_enabled(vcpu)) {
+ to->clean = from->clean;
+ memcpy(to->reserved_sw, from->reserved_sw,
+ sizeof(struct hv_enlightenments));
+ }
}

void nested_copy_vmcb_control_to_cache(struct vcpu_svm *svm,
struct vmcb_control_area *control)
{
- __nested_copy_vmcb_control_to_cache(&svm->nested.ctl, control);
+ __nested_copy_vmcb_control_to_cache(&svm->vcpu, &svm->nested.ctl, control);
}

static void __nested_copy_vmcb_save_to_cache(struct vmcb_save_area_cached *to,
@@ -1305,6 +1331,7 @@ static void nested_copy_vmcb_cache_to_control(struct vmcb_control_area *dst,
dst->virt_ext = from->virt_ext;
dst->pause_filter_count = from->pause_filter_count;
dst->pause_filter_thresh = from->pause_filter_thresh;
+ /* 'clean' and 'reserved_sw' are not changed by KVM */
}

static int svm_get_nested_state(struct kvm_vcpu *vcpu,
@@ -1437,7 +1464,7 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu,
goto out_free;

ret = -EINVAL;
- __nested_copy_vmcb_control_to_cache(&ctl_cached, ctl);
+ __nested_copy_vmcb_control_to_cache(vcpu, &ctl_cached, ctl);
if (!__nested_vmcb_check_controls(vcpu, &ctl_cached))
goto out_free;

diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index e5040daaa968..40b0b92d4e3e 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -138,6 +138,8 @@ struct vmcb_ctrl_area_cached {
u32 event_inj_err;
u64 nested_cr3;
u64 virt_ext;
+ u32 clean;
+ u8 reserved_sw[32];
};

struct svm_nested_state {
--
2.33.1