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Date: Mon, 14 Dec 2020 17:03:00 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Tom Lendacky <thomas.lendacky@....com>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, x86@...nel.org
Cc: Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>,
Sean Christopherson <seanjc@...gle.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
Wanpeng Li <wanpengli@...cent.com>,
Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v5 27/34] KVM: SVM: Add support for booting APs for an
SEV-ES guest
On 10/12/20 18:10, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
>
> Typically under KVM, an AP is booted using the INIT-SIPI-SIPI sequence,
> where the guest vCPU register state is updated and then the vCPU is VMRUN
> to begin execution of the AP. For an SEV-ES guest, this won't work because
> the guest register state is encrypted.
>
> Following the GHCB specification, the hypervisor must not alter the guest
> register state, so KVM must track an AP/vCPU boot. Should the guest want
> to park the AP, it must use the AP Reset Hold exit event in place of, for
> example, a HLT loop.
>
> First AP boot (first INIT-SIPI-SIPI sequence):
> Execute the AP (vCPU) as it was initialized and measured by the SEV-ES
> support. It is up to the guest to transfer control of the AP to the
> proper location.
>
> Subsequent AP boot:
> KVM will expect to receive an AP Reset Hold exit event indicating that
> the vCPU is being parked and will require an INIT-SIPI-SIPI sequence to
> awaken it. When the AP Reset Hold exit event is received, KVM will place
> the vCPU into a simulated HLT mode. Upon receiving the INIT-SIPI-SIPI
> sequence, KVM will make the vCPU runnable. It is again up to the guest
> to then transfer control of the AP to the proper location.
>
> The GHCB specification also requires the hypervisor to save the address of
> an AP Jump Table so that, for example, vCPUs that have been parked by UEFI
> can be started by the OS. Provide support for the AP Jump Table set/get
> exit code.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
> arch/x86/include/asm/kvm_host.h | 2 ++
> arch/x86/kvm/svm/sev.c | 50 +++++++++++++++++++++++++++++++++
> arch/x86/kvm/svm/svm.c | 7 +++++
> arch/x86/kvm/svm/svm.h | 3 ++
> arch/x86/kvm/x86.c | 9 ++++++
> 5 files changed, 71 insertions(+)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 048b08437c33..60a3b9d33407 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1286,6 +1286,8 @@ struct kvm_x86_ops {
>
> void (*migrate_timers)(struct kvm_vcpu *vcpu);
> void (*msr_filter_changed)(struct kvm_vcpu *vcpu);
> +
> + void (*vcpu_deliver_sipi_vector)(struct kvm_vcpu *vcpu, u8 vector);
> };
>
> struct kvm_x86_nested_ops {
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index a7531de760b5..b47285384b1f 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -17,6 +17,8 @@
> #include <linux/processor.h>
> #include <linux/trace_events.h>
>
> +#include <asm/trapnr.h>
> +
> #include "x86.h"
> #include "svm.h"
> #include "cpuid.h"
> @@ -1449,6 +1451,8 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
> if (!ghcb_sw_scratch_is_valid(ghcb))
> goto vmgexit_err;
> break;
> + case SVM_VMGEXIT_AP_HLT_LOOP:
> + case SVM_VMGEXIT_AP_JUMP_TABLE:
> case SVM_VMGEXIT_UNSUPPORTED_EVENT:
> break;
> default:
> @@ -1770,6 +1774,35 @@ int sev_handle_vmgexit(struct vcpu_svm *svm)
> control->exit_info_2,
> svm->ghcb_sa);
> break;
> + case SVM_VMGEXIT_AP_HLT_LOOP:
> + svm->ap_hlt_loop = true;
This value needs to be communicated to userspace. Let's get this right
from the beginning and use a new KVM_MP_STATE_* value instead (perhaps
reuse KVM_MP_STATE_STOPPED but for x86 #define it as
KVM_MP_STATE_AP_HOLD_RECEIVED?).
> @@ -68,6 +68,7 @@ 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 */
> + u64 ap_jump_table; /* SEV-ES AP Jump Table address */
Do you have any plans for migration of this value? How does the guest
ensure that the hypervisor does not screw with it?
Paolo
> + ret = kvm_emulate_halt(&svm->vcpu);
> + break;
> + case SVM_VMGEXIT_AP_JUMP_TABLE: {
> + struct kvm_sev_info *sev = &to_kvm_svm(svm->vcpu.kvm)->sev_info;
> +
> + switch (control->exit_info_1) {
> + case 0:
> + /* Set AP jump table address */
> + sev->ap_jump_table = control->exit_info_2;
> + break;
> + case 1:
> + /* Get AP jump table address */
> + ghcb_set_sw_exit_info_2(ghcb, sev->ap_jump_table);
> + break;
> + default:
> + pr_err("svm: vmgexit: unsupported AP jump table request - exit_info_1=%#llx\n",
> + control->exit_info_1);
> + ghcb_set_sw_exit_info_1(ghcb, 1);
> + ghcb_set_sw_exit_info_2(ghcb,
> + X86_TRAP_UD |
> + SVM_EVTINJ_TYPE_EXEPT |
> + SVM_EVTINJ_VALID);
> + }
> +
> + ret = 1;
> + break;
> + }
> case SVM_VMGEXIT_UNSUPPORTED_EVENT:
> vcpu_unimpl(&svm->vcpu,
> "vmgexit: unsupported event - exit_info_1=%#llx, exit_info_2=%#llx\n",
> @@ -1790,3 +1823,20 @@ int sev_es_string_io(struct vcpu_svm *svm, int size, unsigned int port, int in)
> return kvm_sev_es_string_io(&svm->vcpu, size, port,
> svm->ghcb_sa, svm->ghcb_sa_len, in);
> }
> +
> +void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
> +{
> + struct vcpu_svm *svm = to_svm(vcpu);
> +
> + /* First SIPI: Use the values as initially set by the VMM */
> + if (!svm->ap_hlt_loop)
> + return;
> +
> + /*
> + * Subsequent SIPI: Return from an AP Reset Hold VMGEXIT, where
> + * the guest will set the CS and RIP. Set SW_EXIT_INFO_2 to a
> + * non-zero value.
> + */
> + ghcb_set_sw_exit_info_2(svm->ghcb, 1);
> + svm->ap_hlt_loop = false;
> +}
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 8d22ae25a0f8..2dbc20701ef5 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -4400,6 +4400,11 @@ static bool svm_apic_init_signal_blocked(struct kvm_vcpu *vcpu)
> (vmcb_is_intercept(&svm->vmcb->control, INTERCEPT_INIT));
> }
>
> +static void svm_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
> +{
> + sev_vcpu_deliver_sipi_vector(vcpu, vector);
> +}
> +
> static void svm_vm_destroy(struct kvm *kvm)
> {
> avic_vm_destroy(kvm);
> @@ -4541,6 +4546,8 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
> .apic_init_signal_blocked = svm_apic_init_signal_blocked,
>
> .msr_filter_changed = svm_msr_filter_changed,
> +
> + .vcpu_deliver_sipi_vector = svm_vcpu_deliver_sipi_vector,
> };
>
> static struct kvm_x86_init_ops svm_init_ops __initdata = {
> diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
> index b3f03dede6ac..5d570d5a6a2c 100644
> --- a/arch/x86/kvm/svm/svm.h
> +++ b/arch/x86/kvm/svm/svm.h
> @@ -68,6 +68,7 @@ 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 */
> + u64 ap_jump_table; /* SEV-ES AP Jump Table address */
> };
>
> struct kvm_svm {
> @@ -174,6 +175,7 @@ struct vcpu_svm {
> struct vmcb_save_area *vmsa;
> struct ghcb *ghcb;
> struct kvm_host_map ghcb_map;
> + bool ap_hlt_loop;
>
> /* SEV-ES scratch area support */
> void *ghcb_sa;
> @@ -574,5 +576,6 @@ void sev_hardware_teardown(void);
> 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);
> +void sev_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector);
>
> #endif
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index ddd614a76744..4fd216b61a89 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10144,6 +10144,15 @@ void kvm_vcpu_deliver_sipi_vector(struct kvm_vcpu *vcpu, u8 vector)
> {
> struct kvm_segment cs;
>
> + /*
> + * Guests with protected state can't have their state altered by KVM,
> + * call the vcpu_deliver_sipi_vector() x86 op for processing.
> + */
> + if (vcpu->arch.guest_state_protected) {
> + kvm_x86_ops.vcpu_deliver_sipi_vector(vcpu, vector);
> + return;
> + }
> +
> kvm_get_segment(vcpu, &cs, VCPU_SREG_CS);
> cs.selector = vector << 8;
> cs.base = vector << 12;
>
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