Re: [PATCH v8 13/18] KVM: x86: Introduce new KVM_FEATURE_SEV_LIVE_MIGRATION feature & Custom MSR.

Paolo Bonzini
2020-12-04T11:22:21Z

On 05/05/20 23:19, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@amd.com>
>
> Add new KVM_FEATURE_SEV_LIVE_MIGRATION feature for guest to check
> for host-side support for SEV live migration. Also add a new custom
> MSR_KVM_SEV_LIVE_MIG_EN for guest to enable the SEV live migration
> feature.
>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> ---
> Documentation/virt/kvm/cpuid.rst | 5 +++++
> Documentation/virt/kvm/msr.rst | 10 ++++++++++
> arch/x86/include/uapi/asm/kvm_para.h | 5 +++++
> arch/x86/kvm/svm/sev.c | 14 ++++++++++++++
> arch/x86/kvm/svm/svm.c | 16 ++++++++++++++++
> arch/x86/kvm/svm/svm.h | 2 ++
> 6 files changed, 52 insertions(+)
>
> diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst
> index 01b081f6e7ea..0514523e00cd 100644
> --- a/Documentation/virt/kvm/cpuid.rst
> +++ b/Documentation/virt/kvm/cpuid.rst
> @@ -86,6 +86,11 @@ KVM_FEATURE_PV_SCHED_YIELD 13 guest checks this feature bit
> before using paravirtualized
> sched yield.
>
> +KVM_FEATURE_SEV_LIVE_MIGRATION 14 guest checks this feature bit before
> + using the page encryption state
> + hypercall to notify the page state
> + change
> +
> KVM_FEATURE_CLOCSOURCE_STABLE_BIT 24 host will warn if no guest-side
> per-cpu warps are expeced in
> kvmclock
> diff --git a/Documentation/virt/kvm/msr.rst b/Documentation/virt/kvm/msr.rst
> index 33892036672d..7cd7786bbb03 100644
> --- a/Documentation/virt/kvm/msr.rst
> +++ b/Documentation/virt/kvm/msr.rst
> @@ -319,3 +319,13 @@ data:
>
> KVM guests can request the host not to poll on HLT, for example if
> they are performing polling themselves.
> +
> +MSR_KVM_SEV_LIVE_MIG_EN:
> + 0x4b564d06
> +
> + Control SEV Live Migration features.
> +
> +data:
> + Bit 0 enables (1) or disables (0) host-side SEV Live Migration feature.
> + Bit 1 enables (1) or disables (0) support for SEV Live Migration extensions.
> + All other bits are reserved.

This doesn't say what the feature is or does, and what the extensions
are. As far as I understand bit 0 is a guest->host communication that
it's properly handling the encryption bitmap.

I applied patches -13, this one a bit changed as follows.

diff --git a/Documentation/virt/kvm/cpuid.rst
b/Documentation/virt/kvm/cpuid.rst
index cf62162d4be2..7d82d7da3835 100644
--- a/Documentation/virt/kvm/cpuid.rst
+++ b/Documentation/virt/kvm/cpuid.rst
@@ -96,6 +96,11 @@ KVM_FEATURE_MSI_EXT_DEST_ID 15 guest
checks this feature bit
before using extended
destination
ID bits in MSI address
bits 11-5.

+KVM_FEATURE_ENCRYPTED_VM_BIT 16 guest checks this
feature bit before
+ using the page
encryption state
+ hypercall and encrypted VM
+ features MSR
+
KVM_FEATURE_CLOCKSOURCE_STABLE_BIT 24 host will warn if no
guest-side
per-cpu warps are
expected in
kvmclock
diff --git a/Documentation/virt/kvm/msr.rst b/Documentation/virt/kvm/msr.rst
index e37a14c323d2..02528bc760b8 100644
--- a/Documentation/virt/kvm/msr.rst
+++ b/Documentation/virt/kvm/msr.rst
@@ -376,3 +376,13 @@ data:
write '1' to bit 0 of the MSR, this causes the host to re-scan its queue
and check if there are more notifications pending. The MSR is available
if KVM_FEATURE_ASYNC_PF_INT is present in CPUID.
+
+MSR_KVM_ENC_VM_FEATURE:
+ 0x4b564d08
+
+ Control encrypted VM features.
+
+data:
+ Bit 0 tells the host that the guest is (1) or is not (0)
issuing the
+ ``KVM_HC_PAGE_ENC_STATUS`` hypercall to keep the encrypted bitmap
+ up to date.
diff --git a/arch/x86/include/uapi/asm/kvm_para.h
b/arch/x86/include/uapi/asm/kvm_para.h
index 950afebfba88..3dda6e416a70 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -33,6 +33,7 @@
#define KVM_FEATURE_PV_SCHED_YIELD 13
#define KVM_FEATURE_ASYNC_PF_INT 14
#define KVM_FEATURE_MSI_EXT_DEST_ID 15
+#define KVM_FEATURE_ENCRYPTED_VM 16

#define KVM_HINTS_REALTIME 0

@@ -54,6 +55,7 @@
#define MSR_KVM_POLL_CONTROL 0x4b564d05
#define MSR_KVM_ASYNC_PF_INT 0x4b564d06
#define MSR_KVM_ASYNC_PF_ACK 0x4b564d07
+#define MSR_KVM_ENC_VM_FEATURE 0x4b564d08

struct kvm_steal_time {
__u64 steal;
@@ -136,4 +138,6 @@ struct kvm_vcpu_pv_apf_data {
#define KVM_PV_EOI_ENABLED KVM_PV_EOI_MASK
#define KVM_PV_EOI_DISABLED 0x0

+#define KVM_ENC_VM_BITMAP_VALID (1 << 0)
+
#endif /* _UAPI_ASM_X86_KVM_PARA_H */
diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index fa67f498e838..0673531233da 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -1478,6 +1478,17 @@ int svm_page_enc_status_hc(struct kvm *kvm,
unsigned long gpa,
return 0;
}

+void sev_update_enc_vm_flags(struct kvm *kvm, u64 data)
+{
+ struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
+
+ if (!sev_guest(kvm))
+ return;
+
+ if (data & KVM_ENC_VM_BITMAP_VALID)
+ sev->live_migration_enabled = true;
+}
+
int svm_get_page_enc_bitmap(struct kvm *kvm,
struct kvm_page_enc_bitmap *bmap)
{
@@ -1490,6 +1501,9 @@ int svm_get_page_enc_bitmap(struct kvm *kvm,
if (!sev_guest(kvm))
return -ENOTTY;

+ if (!sev->live_migration_enabled)
+ return -EINVAL;
+
gfn_start = bmap->start_gfn;
gfn_end = gfn_start + bmap->num_pages;

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 66f7014eaae2..8ac2c5b9c675 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2766,6 +2766,9 @@ static int svm_set_msr(struct kvm_vcpu *vcpu,
struct msr_data *msr)
svm->msr_decfg = data;
break;
}
+ case MSR_KVM_ENC_VM_FEATURE:
+ sev_update_enc_vm_flags(vcpu->kvm, data);
+ break;
case MSR_IA32_APICBASE:
if (kvm_vcpu_apicv_active(vcpu))
avic_update_vapic_bar(to_svm(vcpu), data);
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 287559b8c5b2..363c3f8d00b7 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -66,6 +66,7 @@ struct kvm_sev_info {
int fd; /* SEV device fd */
unsigned long pages_locked; /* Number of pages locked */
struct list_head regions_list; /* List of registered regions */
+ bool live_migration_enabled;
unsigned long *page_enc_bmap;
unsigned long page_enc_bmap_size;
};
@@ -504,5 +505,6 @@ int svm_page_enc_status_hc(struct kvm *kvm, unsigned
long gpa,
unsigned long npages, unsigned long enc);
int svm_get_page_enc_bitmap(struct kvm *kvm, struct
kvm_page_enc_bitmap *bmap);
int svm_set_page_enc_bitmap(struct kvm *kvm, struct
kvm_page_enc_bitmap *bmap);
+void sev_update_enc_vm_flags(struct kvm *kvm, u64 data);

#endif

Paolo