Re: [PATCH v6 12/14] KVM: x86: Introduce KVM_PAGE_ENC_BITMAP_RESET ioctl

[Steve Rutherford]

On Mon, Apr 6, 2020 at 11:53 AM Krish Sadhukhan
<krish.sadhukhan@xxxxxxxxxx> wrote:
>
>
> On 4/3/20 2:45 PM, Ashish Kalra wrote:
> > On Fri, Apr 03, 2020 at 02:14:23PM -0700, Krish Sadhukhan wrote:
> >> On 3/29/20 11:23 PM, Ashish Kalra wrote:
> >>> From: Ashish Kalra <ashish.kalra@xxxxxxx>
> >>>
> >>> This ioctl can be used by the application to reset the page
> >>> encryption bitmap managed by the KVM driver. A typical usage
> >>> for this ioctl is on VM reboot, on reboot, we must reinitialize
> >>> the bitmap.
> >>>
> >>> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> >>> ---
> >>>    Documentation/virt/kvm/api.rst  | 13 +++++++++++++
> >>>    arch/x86/include/asm/kvm_host.h |  1 +
> >>>    arch/x86/kvm/svm.c              | 16 ++++++++++++++++
> >>>    arch/x86/kvm/x86.c              |  6 ++++++
> >>>    include/uapi/linux/kvm.h        |  1 +
> >>>    5 files changed, 37 insertions(+)
> >>>
> >>> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> >>> index 4d1004a154f6..a11326ccc51d 100644
> >>> --- a/Documentation/virt/kvm/api.rst
> >>> +++ b/Documentation/virt/kvm/api.rst
> >>> @@ -4698,6 +4698,19 @@ During the guest live migration the outgoing guest exports its page encryption
> >>>    bitmap, the KVM_SET_PAGE_ENC_BITMAP can be used to build the page encryption
> >>>    bitmap for an incoming guest.
> >>> +4.127 KVM_PAGE_ENC_BITMAP_RESET (vm ioctl)
> >>> +-----------------------------------------
> >>> +
> >>> +:Capability: basic
> >>> +:Architectures: x86
> >>> +:Type: vm ioctl
> >>> +:Parameters: none
> >>> +:Returns: 0 on success, -1 on error
> >>> +
> >>> +The KVM_PAGE_ENC_BITMAP_RESET is used to reset the guest's page encryption
> >>> +bitmap during guest reboot and this is only done on the guest's boot vCPU.
> >>> +
> >>> +
> >>>    5. The kvm_run structure
> >>>    ========================
> >>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> >>> index d30f770aaaea..a96ef6338cd2 100644
> >>> --- a/arch/x86/include/asm/kvm_host.h
> >>> +++ b/arch/x86/include/asm/kvm_host.h
> >>> @@ -1273,6 +1273,7 @@ struct kvm_x86_ops {
> >>>                             struct kvm_page_enc_bitmap *bmap);
> >>>     int (*set_page_enc_bitmap)(struct kvm *kvm,
> >>>                             struct kvm_page_enc_bitmap *bmap);
> >>> +   int (*reset_page_enc_bitmap)(struct kvm *kvm);
> >>>    };
> >>>    struct kvm_arch_async_pf {
> >>> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> >>> index 313343a43045..c99b0207a443 100644
> >>> --- a/arch/x86/kvm/svm.c
> >>> +++ b/arch/x86/kvm/svm.c
> >>> @@ -7797,6 +7797,21 @@ static int svm_set_page_enc_bitmap(struct kvm *kvm,
> >>>     return ret;
> >>>    }
> >>> +static int svm_reset_page_enc_bitmap(struct kvm *kvm)
> >>> +{
> >>> +   struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> >>> +
> >>> +   if (!sev_guest(kvm))
> >>> +           return -ENOTTY;
> >>> +
> >>> +   mutex_lock(&kvm->lock);
> >>> +   /* by default all pages should be marked encrypted */
> >>> +   if (sev->page_enc_bmap_size)
> >>> +           bitmap_fill(sev->page_enc_bmap, sev->page_enc_bmap_size);
> >>> +   mutex_unlock(&kvm->lock);
> >>> +   return 0;
> >>> +}
> >>> +
> >>>    static int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
> >>>    {
> >>>     struct kvm_sev_cmd sev_cmd;
> >>> @@ -8203,6 +8218,7 @@ static struct kvm_x86_ops svm_x86_ops __ro_after_init = {
> >>>     .page_enc_status_hc = svm_page_enc_status_hc,
> >>>     .get_page_enc_bitmap = svm_get_page_enc_bitmap,
> >>>     .set_page_enc_bitmap = svm_set_page_enc_bitmap,
> >>> +   .reset_page_enc_bitmap = svm_reset_page_enc_bitmap,
> >>
> >> We don't need to initialize the intel ops to NULL ? It's not initialized in
> >> the previous patch either.
> >>
> >>>    };
> > This struct is declared as "static storage", so won't the non-initialized
> > members be 0 ?
>
>
> Correct. Although, I see that 'nested_enable_evmcs' is explicitly
> initialized. We should maintain the convention, perhaps.
>
> >
> >>>    static int __init svm_init(void)
> >>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> >>> index 05e953b2ec61..2127ed937f53 100644
> >>> --- a/arch/x86/kvm/x86.c
> >>> +++ b/arch/x86/kvm/x86.c
> >>> @@ -5250,6 +5250,12 @@ long kvm_arch_vm_ioctl(struct file *filp,
> >>>                     r = kvm_x86_ops->set_page_enc_bitmap(kvm, &bitmap);
> >>>             break;
> >>>     }
> >>> +   case KVM_PAGE_ENC_BITMAP_RESET: {
> >>> +           r = -ENOTTY;
> >>> +           if (kvm_x86_ops->reset_page_enc_bitmap)
> >>> +                   r = kvm_x86_ops->reset_page_enc_bitmap(kvm);
> >>> +           break;
> >>> +   }
> >>>     default:
> >>>             r = -ENOTTY;
> >>>     }
> >>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> >>> index b4b01d47e568..0884a581fc37 100644
> >>> --- a/include/uapi/linux/kvm.h
> >>> +++ b/include/uapi/linux/kvm.h
> >>> @@ -1490,6 +1490,7 @@ struct kvm_enc_region {
> >>>    #define KVM_GET_PAGE_ENC_BITMAP  _IOW(KVMIO, 0xc5, struct kvm_page_enc_bitmap)
> >>>    #define KVM_SET_PAGE_ENC_BITMAP  _IOW(KVMIO, 0xc6, struct kvm_page_enc_bitmap)
> >>> +#define KVM_PAGE_ENC_BITMAP_RESET  _IO(KVMIO, 0xc7)
> >>>    /* Secure Encrypted Virtualization command */
> >>>    enum sev_cmd_id {
> >> Reviewed-by: Krish Sadhukhan <krish.sadhukhan@xxxxxxxxxx>


Doesn't this overlap with the set ioctl? Yes, obviously, you have to
copy the new value down and do a bit more work, but I don't think
resetting the bitmap is going to be the bottleneck on reboot. Seems
excessive to add another ioctl for this.