Re: [PATCH v13 10/12] KVM: x86: Introduce new KVM_FEATURE_SEV_LIVE_MIGRATION feature & Custom MSR.

[Paolo Bonzini <pbonzini@redhat.com>]

On 15/04/21 17:58, 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_MIGRATION for guest to enable the SEV live migration
> feature.
> 
> MSR is handled by userspace using MSR filters.
> 
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> Reviewed-by: Steve Rutherford <srutherford@google.com>

Let's leave the MSR out for now and rename the feature to 
KVM_FEATURE_HC_PAGE_ENC_STATUS.

Paolo

> ---
>   Documentation/virt/kvm/cpuid.rst     |  5 +++++
>   Documentation/virt/kvm/msr.rst       | 12 ++++++++++++
>   arch/x86/include/uapi/asm/kvm_para.h |  4 ++++
>   arch/x86/kvm/cpuid.c                 |  3 ++-
>   4 files changed, 23 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst
> index cf62162d4be2..0bdb6cdb12d3 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_SEV_LIVE_MIGRATION     16          guest checks this feature bit before
> +                                               using the page encryption state
> +                                               hypercall to notify the page state
> +                                               change
> +
>   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..020245d16087 100644
> --- a/Documentation/virt/kvm/msr.rst
> +++ b/Documentation/virt/kvm/msr.rst
> @@ -376,3 +376,15 @@ 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_SEV_LIVE_MIGRATION:
> +        0x4b564d08
> +
> +	Control SEV Live Migration features.
> +
> +data:
> +        Bit 0 enables (1) or disables (0) host-side SEV Live Migration feature,
> +        in other words, this is guest->host communication that it's properly
> +        handling the shared pages list.
> +
> +        All other bits are reserved.
> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
> index 950afebfba88..f6bfa138874f 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_SEV_LIVE_MIGRATION	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_SEV_LIVE_MIGRATION	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_SEV_LIVE_MIGRATION_ENABLED BIT_ULL(0)
> +
>   #endif /* _UAPI_ASM_X86_KVM_PARA_H */
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 6bd2f8b830e4..4e2e69a692aa 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -812,7 +812,8 @@ static inline int __do_cpuid_func(struct kvm_cpuid_array *array, u32 function)
>   			     (1 << KVM_FEATURE_PV_SEND_IPI) |
>   			     (1 << KVM_FEATURE_POLL_CONTROL) |
>   			     (1 << KVM_FEATURE_PV_SCHED_YIELD) |
> -			     (1 << KVM_FEATURE_ASYNC_PF_INT);
> +			     (1 << KVM_FEATURE_ASYNC_PF_INT) |
> +			     (1 << KVM_FEATURE_SEV_LIVE_MIGRATION);
>   
>   		if (sched_info_on())
>   			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
>