Re: [PATCH v6 13/14] KVM: x86: Introduce new KVM_FEATURE_SEV_LIVE_MIGRATION feature & Custom MSR.

[Krish Sadhukhan]

On 3/29/20 11:23 PM, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@xxxxxxx>
>
> 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.
>
> Also, ensure that _bss_decrypted section is marked as decrypted in the
> page encryption bitmap.
>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> ---
>   Documentation/virt/kvm/cpuid.rst     |  4 ++++
>   Documentation/virt/kvm/msr.rst       | 10 ++++++++++
>   arch/x86/include/asm/kvm_host.h      |  3 +++
>   arch/x86/include/uapi/asm/kvm_para.h |  5 +++++
>   arch/x86/kernel/kvm.c                |  4 ++++
>   arch/x86/kvm/cpuid.c                 |  3 ++-
>   arch/x86/kvm/svm.c                   |  5 +++++
>   arch/x86/kvm/x86.c                   |  7 +++++++
>   arch/x86/mm/mem_encrypt.c            | 14 +++++++++++++-
>   9 files changed, 53 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/virt/kvm/cpuid.rst b/Documentation/virt/kvm/cpuid.rst
> index 01b081f6e7ea..fcb191bb3016 100644
> --- a/Documentation/virt/kvm/cpuid.rst
> +++ b/Documentation/virt/kvm/cpuid.rst
> @@ -86,6 +86,10 @@ 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 enabling SEV live
> +                                              migration feature.
> +
>   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.
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index a96ef6338cd2..ad5faaed43c0 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -780,6 +780,9 @@ struct kvm_vcpu_arch {
>   
>   	u64 msr_kvm_poll_control;
>   
> +	/* SEV Live Migration MSR (AMD only) */
> +	u64 msr_kvm_sev_live_migration_flag;
> +
>   	/*
>   	 * Indicates the guest is trying to write a gfn that contains one or
>   	 * more of the PTEs used to translate the write itself, i.e. the access
> diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
> index 2a8e0b6b9805..d9d4953b42ad 100644
> --- a/arch/x86/include/uapi/asm/kvm_para.h
> +++ b/arch/x86/include/uapi/asm/kvm_para.h
> @@ -31,6 +31,7 @@
>   #define KVM_FEATURE_PV_SEND_IPI	11
>   #define KVM_FEATURE_POLL_CONTROL	12
>   #define KVM_FEATURE_PV_SCHED_YIELD	13
> +#define KVM_FEATURE_SEV_LIVE_MIGRATION	14
>   
>   #define KVM_HINTS_REALTIME      0
>   
> @@ -50,6 +51,7 @@
>   #define MSR_KVM_STEAL_TIME  0x4b564d03
>   #define MSR_KVM_PV_EOI_EN      0x4b564d04
>   #define MSR_KVM_POLL_CONTROL	0x4b564d05
> +#define MSR_KVM_SEV_LIVE_MIG_EN	0x4b564d06
>   
>   struct kvm_steal_time {
>   	__u64 steal;
> @@ -122,4 +124,7 @@ 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			(1 << 0)
> +#define KVM_SEV_LIVE_MIGRATION_EXTENSIONS_SUPPORTED	(1 << 1)
> +
>   #endif /* _UAPI_ASM_X86_KVM_PARA_H */
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 6efe0410fb72..8fcee0b45231 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -418,6 +418,10 @@ static void __init sev_map_percpu_data(void)
>   	if (!sev_active())
>   		return;
>   
> +	if (kvm_para_has_feature(KVM_FEATURE_SEV_LIVE_MIGRATION)) {
> +		wrmsrl(MSR_KVM_SEV_LIVE_MIG_EN, KVM_SEV_LIVE_MIGRATION_ENABLED);
> +	}
> +
>   	for_each_possible_cpu(cpu) {
>   		__set_percpu_decrypted(&per_cpu(apf_reason, cpu), sizeof(apf_reason));
>   		__set_percpu_decrypted(&per_cpu(steal_time, cpu), sizeof(steal_time));
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index b1c469446b07..74c8b2a7270c 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -716,7 +716,8 @@ static inline int __do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 function,
>   			     (1 << KVM_FEATURE_ASYNC_PF_VMEXIT) |
>   			     (1 << KVM_FEATURE_PV_SEND_IPI) |
>   			     (1 << KVM_FEATURE_POLL_CONTROL) |
> -			     (1 << KVM_FEATURE_PV_SCHED_YIELD);
> +			     (1 << KVM_FEATURE_PV_SCHED_YIELD) |
> +			     (1 << KVM_FEATURE_SEV_LIVE_MIGRATION);
>   
>   		if (sched_info_on())
>   			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index c99b0207a443..60ddc242a133 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -7632,6 +7632,7 @@ static int svm_page_enc_status_hc(struct kvm *kvm, unsigned long gpa,
>   				  unsigned long npages, unsigned long enc)
>   {
>   	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +	struct kvm_vcpu *vcpu = kvm->vcpus[0];
>   	kvm_pfn_t pfn_start, pfn_end;
>   	gfn_t gfn_start, gfn_end;
>   	int ret;
> @@ -7639,6 +7640,10 @@ static int svm_page_enc_status_hc(struct kvm *kvm, unsigned long gpa,
>   	if (!sev_guest(kvm))
>   		return -EINVAL;
>   
> +	if (!(vcpu->arch.msr_kvm_sev_live_migration_flag &
> +		KVM_SEV_LIVE_MIGRATION_ENABLED))
> +		return -ENOTTY;
> +
>   	if (!npages)
>   		return 0;
>   
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 2127ed937f53..82867b8798f8 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -2880,6 +2880,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		vcpu->arch.msr_kvm_poll_control = data;
>   		break;
>   
> +	case MSR_KVM_SEV_LIVE_MIG_EN:
> +		vcpu->arch.msr_kvm_sev_live_migration_flag = data;
> +		break;
> +
>   	case MSR_IA32_MCG_CTL:
>   	case MSR_IA32_MCG_STATUS:
>   	case MSR_IA32_MC0_CTL ... MSR_IA32_MCx_CTL(KVM_MAX_MCE_BANKS) - 1:
> @@ -3126,6 +3130,9 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   	case MSR_KVM_POLL_CONTROL:
>   		msr_info->data = vcpu->arch.msr_kvm_poll_control;
>   		break;
> +	case MSR_KVM_SEV_LIVE_MIG_EN:
> +		msr_info->data = vcpu->arch.msr_kvm_sev_live_migration_flag;
> +		break;
>   	case MSR_IA32_P5_MC_ADDR:
>   	case MSR_IA32_P5_MC_TYPE:
>   	case MSR_IA32_MCG_CAP:
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index c9800fa811f6..f6a841494845 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -502,8 +502,20 @@ void __init mem_encrypt_init(void)
>   	 * With SEV, we need to make a hypercall when page encryption state is
>   	 * changed.
>   	 */
> -	if (sev_active())
> +	if (sev_active()) {
> +		unsigned long nr_pages;
> +
>   		pv_ops.mmu.page_encryption_changed = set_memory_enc_dec_hypercall;
> +
> +		/*
> +		 * Ensure that _bss_decrypted section is marked as decrypted in the
> +		 * page encryption bitmap.
> +		 */
> +		nr_pages = DIV_ROUND_UP(__end_bss_decrypted - __start_bss_decrypted,
> +			PAGE_SIZE);
> +		set_memory_enc_dec_hypercall((unsigned long)__start_bss_decrypted,
> +			nr_pages, 0);
> +	}
>   #endif
>   
>   	pr_info("AMD %s active\n",
Reviewed-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>