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Date: Thu, 4 Feb 2021 16:56:35 -0800
From: Steve Rutherford <srutherford@...gle.com>
To: Ashish Kalra <Ashish.Kalra@....com>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...e.de>,
Tom Lendacky <thomas.lendacky@....com>,
X86 ML <x86@...nel.org>, KVM list <kvm@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Sean Christopherson <seanjc@...gle.com>,
Venu Busireddy <venu.busireddy@...cle.com>,
Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v10 12/16] KVM: x86: Introduce new KVM_FEATURE_SEV_LIVE_MIGRATION
feature & Custom MSR.
On Wed, Feb 3, 2021 at 4:39 PM Ashish Kalra <Ashish.Kalra@....com> wrote:
>
> From: Ashish Kalra <ashish.kalra@....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.
>
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>
> ---
> Documentation/virt/kvm/cpuid.rst | 5 +++++
> Documentation/virt/kvm/msr.rst | 12 ++++++++++++
> arch/x86/include/uapi/asm/kvm_para.h | 4 ++++
> arch/x86/kvm/svm/sev.c | 13 +++++++++++++
> 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 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/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index b0d324aed515..93f42b3d3e33 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -1627,6 +1627,16 @@ int svm_page_enc_status_hc(struct kvm *kvm, unsigned long gpa,
> return ret;
> }
>
> +void sev_update_migration_flags(struct kvm *kvm, u64 data)
> +{
> + struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> +
> + if (!sev_guest(kvm))
> + return;
This should assert that userspace wanted the guest to be able to make
these calls (see more below).
>
> +
> + sev->live_migration_enabled = !!(data & KVM_SEV_LIVE_MIGRATION_ENABLED);
> +}
> +
> int svm_get_shared_pages_list(struct kvm *kvm,
> struct kvm_shared_pages_list *list)
> {
> @@ -1639,6 +1649,9 @@ int svm_get_shared_pages_list(struct kvm *kvm,
> if (!sev_guest(kvm))
> return -ENOTTY;
>
> + if (!sev->live_migration_enabled)
> + return -EINVAL;
> +
> if (!list->size)
> return -EINVAL;
>
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 58f89f83caab..43ea5061926f 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2903,6 +2903,9 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
> svm->msr_decfg = data;
> break;
> }
> + case MSR_KVM_SEV_LIVE_MIGRATION:
> + sev_update_migration_flags(vcpu->kvm, data);
> + break;
> case MSR_IA32_APICBASE:
> if (kvm_vcpu_apicv_active(vcpu))
> avic_update_vapic_bar(to_svm(vcpu), data);
> @@ -3976,6 +3979,19 @@ static void svm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> vcpu->arch.cr3_lm_rsvd_bits &= ~(1UL << (best->ebx & 0x3f));
> }
>
> + /*
> + * If SEV guest then enable the Live migration feature.
> + */
> + if (sev_guest(vcpu->kvm)) {
> + struct kvm_cpuid_entry2 *best;
> +
> + best = kvm_find_cpuid_entry(vcpu, KVM_CPUID_FEATURES, 0);
> + if (!best)
> + return;
> +
> + best->eax |= (1 << KVM_FEATURE_SEV_LIVE_MIGRATION);
> + }
> +
Looking at this, I believe the only way for this bit to get enabled is
if userspace toggles it. There needs to be a way for userspace to
identify if the kernel underneath them does, in fact, support SEV LM.
I'm at risk for having misread these patches (it's a long series), but
I don't see anything that communicates upwards.
This could go upward with the other paravirt features flags in
cpuid.c. It could also be an explicit KVM Capability (checked through
check_extension).
Userspace should then have a chance to decide whether or not this
should be enabled. And when it's not enabled, the host should return a
GP in response to the hypercall. This could be configured either
through userspace stripping out the LM feature bit, or by calling a VM
scoped enable cap (KVM_VM_IOCTL_ENABLE_CAP).
I believe the typical path for a feature like this to be configured
would be to use ENABLE_CAP.
>
> if (!kvm_vcpu_apicv_active(vcpu))
> return;
>
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index 066ca2a9f1e6..e1bffc11e425 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -79,6 +79,7 @@ struct kvm_sev_info {
> unsigned long pages_locked; /* Number of pages locked */
> struct list_head regions_list; /* List of registered regions */
> u64 ap_jump_table; /* SEV-ES AP Jump Table address */
> + bool live_migration_enabled;
> /* List and count of shared pages */
> int shared_pages_list_count;
> struct list_head shared_pages_list;
> @@ -592,6 +593,7 @@ int svm_unregister_enc_region(struct kvm *kvm,
> void pre_sev_run(struct vcpu_svm *svm, int cpu);
> void __init sev_hardware_setup(void);
> void sev_hardware_teardown(void);
> +void sev_update_migration_flags(struct kvm *kvm, u64 data);
> void sev_free_vcpu(struct kvm_vcpu *vcpu);
> int sev_handle_vmgexit(struct vcpu_svm *svm);
> int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in);
> --
> 2.17.1
>
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