Re: [PATCH v12 08/13] KVM: X86: Introduce KVM_HC_PAGE_ENC_STATUS hypercall

[Steve Rutherford <srutherford@google.com>]

On Mon, Apr 12, 2021 at 12:45 PM Ashish Kalra <Ashish.Kalra@amd.com> wrote:
>
> From: Ashish Kalra <ashish.kalra@amd.com>
>
> This hypercall is used by the SEV guest to notify a change in the page
> encryption status to the hypervisor. The hypercall should be invoked
> only when the encryption attribute is changed from encrypted -> decrypted
> and vice versa. By default all guest pages are considered encrypted.
>
> The hypercall exits to userspace to manage the guest shared regions and
> integrate with the userspace VMM's migration code.
>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Joerg Roedel <joro@8bytes.org>
> Cc: Borislav Petkov <bp@suse.de>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: x86@kernel.org
> Cc: kvm@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> Co-developed-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>  Documentation/virt/kvm/hypercalls.rst | 15 ++++++++++++++
>  arch/x86/include/asm/kvm_host.h       |  2 ++
>  arch/x86/kvm/svm/sev.c                |  1 +
>  arch/x86/kvm/x86.c                    | 29 +++++++++++++++++++++++++++
>  include/uapi/linux/kvm_para.h         |  1 +
>  5 files changed, 48 insertions(+)
>
> diff --git a/Documentation/virt/kvm/hypercalls.rst b/Documentation/virt/kvm/hypercalls.rst
> index ed4fddd364ea..7aff0cebab7c 100644
> --- a/Documentation/virt/kvm/hypercalls.rst
> +++ b/Documentation/virt/kvm/hypercalls.rst
> @@ -169,3 +169,18 @@ a0: destination APIC ID
>
>  :Usage example: When sending a call-function IPI-many to vCPUs, yield if
>                 any of the IPI target vCPUs was preempted.
> +
> +
> +8. KVM_HC_PAGE_ENC_STATUS
> +-------------------------
> +:Architecture: x86
> +:Status: active
> +:Purpose: Notify the encryption status changes in guest page table (SEV guest)
> +
> +a0: the guest physical address of the start page
> +a1: the number of pages
> +a2: encryption attribute
> +
> +   Where:
> +       * 1: Encryption attribute is set
> +       * 0: Encryption attribute is cleared
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 3768819693e5..42eb0fe3df5d 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1050,6 +1050,8 @@ struct kvm_arch {
>
>         bool bus_lock_detection_enabled;
>
> +       bool page_enc_hc_enable;
> +
>         /* Deflect RDMSR and WRMSR to user space when they trigger a #GP */
>         u32 user_space_msr_mask;
>         struct kvm_x86_msr_filter __rcu *msr_filter;
> diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
> index c9795a22e502..5184a0c0131a 100644
> --- a/arch/x86/kvm/svm/sev.c
> +++ b/arch/x86/kvm/svm/sev.c
> @@ -197,6 +197,7 @@ static int sev_guest_init(struct kvm *kvm, struct kvm_sev_cmd *argp)
>         sev->active = true;
>         sev->asid = asid;
>         INIT_LIST_HEAD(&sev->regions_list);
> +       kvm->arch.page_enc_hc_enable = true;
>
>         return 0;
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f7d12fca397b..e8986478b653 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8208,6 +8208,13 @@ static void kvm_sched_yield(struct kvm *kvm, unsigned long dest_id)
>                 kvm_vcpu_yield_to(target);
>  }
>
> +static int complete_hypercall_exit(struct kvm_vcpu *vcpu)
> +{
> +       kvm_rax_write(vcpu, vcpu->run->hypercall.ret);
> +       ++vcpu->stat.hypercalls;
> +       return kvm_skip_emulated_instruction(vcpu);
> +}
> +
>  int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>  {
>         unsigned long nr, a0, a1, a2, a3, ret;
> @@ -8273,6 +8280,28 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
>                 kvm_sched_yield(vcpu->kvm, a0);
>                 ret = 0;
>                 break;
> +       case KVM_HC_PAGE_ENC_STATUS: {
> +               u64 gpa = a0, npages = a1, enc = a2;
> +
> +               ret = -KVM_ENOSYS;
> +               if (!vcpu->kvm->arch.page_enc_hc_enable)
> +                       break;
> +
> +               if (!PAGE_ALIGNED(gpa) || !npages ||
> +                   gpa_to_gfn(gpa) + npages <= gpa_to_gfn(gpa)) {
> +                       ret = -EINVAL;
> +                       break;
> +               }
> +
> +               vcpu->run->exit_reason        = KVM_EXIT_HYPERCALL;
> +               vcpu->run->hypercall.nr       = KVM_HC_PAGE_ENC_STATUS;
> +               vcpu->run->hypercall.args[0]  = gpa;
> +               vcpu->run->hypercall.args[1]  = npages;
> +               vcpu->run->hypercall.args[2]  = enc;
> +               vcpu->run->hypercall.longmode = op_64_bit;
> +               vcpu->arch.complete_userspace_io = complete_hypercall_exit;
> +               return 0;
> +       }
>         default:
>                 ret = -KVM_ENOSYS;
>                 break;
> diff --git a/include/uapi/linux/kvm_para.h b/include/uapi/linux/kvm_para.h
> index 8b86609849b9..847b83b75dc8 100644
> --- a/include/uapi/linux/kvm_para.h
> +++ b/include/uapi/linux/kvm_para.h
> @@ -29,6 +29,7 @@
>  #define KVM_HC_CLOCK_PAIRING           9
>  #define KVM_HC_SEND_IPI                10
>  #define KVM_HC_SCHED_YIELD             11
> +#define KVM_HC_PAGE_ENC_STATUS         12
>
>  /*
>   * hypercalls use architecture specific
> --
> 2.17.1
>
Reviewed-by: Steve Rutherford <srutherford@google.com>