Re: [PATCH v6 11/14] KVM: x86: Introduce KVM_SET_PAGE_ENC_BITMAP ioctl

[Ashish Kalra <ashish.kalra@amd.com>]

Hello Steve,

On Tue, Apr 07, 2020 at 05:26:33PM -0700, Steve Rutherford wrote:
> On Sun, Mar 29, 2020 at 11:23 PM Ashish Kalra <Ashish.Kalra@amd.com> wrote:
> >
> > From: Brijesh Singh <Brijesh.Singh@amd.com>
> >
> > The ioctl can be used to set page encryption bitmap for an
> > incoming guest.
> >
> > 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: "Radim Krčmář" <rkrcmar@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>
> > ---
> >  Documentation/virt/kvm/api.rst  | 22 +++++++++++++++++
> >  arch/x86/include/asm/kvm_host.h |  2 ++
> >  arch/x86/kvm/svm.c              | 42 +++++++++++++++++++++++++++++++++
> >  arch/x86/kvm/x86.c              | 12 ++++++++++
> >  include/uapi/linux/kvm.h        |  1 +
> >  5 files changed, 79 insertions(+)
> >
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index 8ad800ebb54f..4d1004a154f6 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -4675,6 +4675,28 @@ or shared. The bitmap can be used during the guest migration, if the page
> >  is private then userspace need to use SEV migration commands to transmit
> >  the page.
> >
> > +4.126 KVM_SET_PAGE_ENC_BITMAP (vm ioctl)
> > +---------------------------------------
> > +
> > +:Capability: basic
> > +:Architectures: x86
> > +:Type: vm ioctl
> > +:Parameters: struct kvm_page_enc_bitmap (in/out)
> > +:Returns: 0 on success, -1 on error
> > +
> > +/* for KVM_SET_PAGE_ENC_BITMAP */
> > +struct kvm_page_enc_bitmap {
> > +       __u64 start_gfn;
> > +       __u64 num_pages;
> > +       union {
> > +               void __user *enc_bitmap; /* one bit per page */
> > +               __u64 padding2;
> > +       };
> > +};
> > +
> > +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.
> >
> >  5. The kvm_run structure
> >  ========================
> > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> > index 27e43e3ec9d8..d30f770aaaea 100644
> > --- a/arch/x86/include/asm/kvm_host.h
> > +++ b/arch/x86/include/asm/kvm_host.h
> > @@ -1271,6 +1271,8 @@ struct kvm_x86_ops {
> >                                   unsigned long sz, unsigned long mode);
> >         int (*get_page_enc_bitmap)(struct kvm *kvm,
> >                                 struct kvm_page_enc_bitmap *bmap);
> > +       int (*set_page_enc_bitmap)(struct kvm *kvm,
> > +                               struct kvm_page_enc_bitmap *bmap);
> >  };
> >
> >  struct kvm_arch_async_pf {
> > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> > index bae783cd396a..313343a43045 100644
> > --- a/arch/x86/kvm/svm.c
> > +++ b/arch/x86/kvm/svm.c
> > @@ -7756,6 +7756,47 @@ static int svm_get_page_enc_bitmap(struct kvm *kvm,
> >         return ret;
> >  }
> >
> > +static int svm_set_page_enc_bitmap(struct kvm *kvm,
> > +                                  struct kvm_page_enc_bitmap *bmap)
> > +{
> > +       struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
> > +       unsigned long gfn_start, gfn_end;
> > +       unsigned long *bitmap;
> > +       unsigned long sz, i;
> > +       int ret;
> > +
> > +       if (!sev_guest(kvm))
> > +               return -ENOTTY;
> > +
> > +       gfn_start = bmap->start_gfn;
> > +       gfn_end = gfn_start + bmap->num_pages;
> > +
> > +       sz = ALIGN(bmap->num_pages, BITS_PER_LONG) / 8;
> > +       bitmap = kmalloc(sz, GFP_KERNEL);
> > +       if (!bitmap)
> > +               return -ENOMEM;
> > +
> > +       ret = -EFAULT;
> > +       if (copy_from_user(bitmap, bmap->enc_bitmap, sz))
> > +               goto out;
> > +
> > +       mutex_lock(&kvm->lock);
> > +       ret = sev_resize_page_enc_bitmap(kvm, gfn_end);
> I realize now that usermode could use this for initializing the
> minimum size of the enc bitmap, which probably solves my issue from
> the other thread.
> > +       if (ret)
> > +               goto unlock;
> > +
> > +       i = gfn_start;
> > +       for_each_clear_bit_from(i, bitmap, (gfn_end - gfn_start))
> > +               clear_bit(i + gfn_start, sev->page_enc_bmap);
> This API seems a bit strange, since it can only clear bits. I would
> expect "set" to force the values to match the values passed down,
> instead of only ensuring that cleared bits in the input are also
> cleared in the kernel.
>

The sev_resize_page_enc_bitmap() will allocate a new bitmap and
set it to all 0xFF's, therefore, the code here simply clears the bits
in the bitmap as per the cleared bits in the input.

Thanks,
Ashish

> This should copy the values from userspace (and fix up the ends since
> byte alignment makes that complicated), instead of iterating in this
> way.
> > +
> > +       ret = 0;
> > +unlock:
> > +       mutex_unlock(&kvm->lock);
> > +out:
> > +       kfree(bitmap);
> > +       return ret;
> > +}
> > +
> >  static int svm_mem_enc_op(struct kvm *kvm, void __user *argp)
> >  {
> >         struct kvm_sev_cmd sev_cmd;
> > @@ -8161,6 +8202,7 @@ 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,
> >  };
> >
> >  static int __init svm_init(void)
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 3c3fea4e20b5..05e953b2ec61 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -5238,6 +5238,18 @@ long kvm_arch_vm_ioctl(struct file *filp,
> >                         r = kvm_x86_ops->get_page_enc_bitmap(kvm, &bitmap);
> >                 break;
> >         }
> > +       case KVM_SET_PAGE_ENC_BITMAP: {
> > +               struct kvm_page_enc_bitmap bitmap;
> > +
> > +               r = -EFAULT;
> > +               if (copy_from_user(&bitmap, argp, sizeof(bitmap)))
> > +                       goto out;
> > +
> > +               r = -ENOTTY;
> > +               if (kvm_x86_ops->set_page_enc_bitmap)
> > +                       r = kvm_x86_ops->set_page_enc_bitmap(kvm, &bitmap);
> > +               break;
> > +       }
> >         default:
> >                 r = -ENOTTY;
> >         }
> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > index db1ebf85e177..b4b01d47e568 100644
> > --- a/include/uapi/linux/kvm.h
> > +++ b/include/uapi/linux/kvm.h
> > @@ -1489,6 +1489,7 @@ struct kvm_enc_region {
> >  #define KVM_S390_CLEAR_RESET   _IO(KVMIO,   0xc4)
> >
> >  #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)
> >
> >  /* Secure Encrypted Virtualization command */
> >  enum sev_cmd_id {
> > --
> > 2.17.1
> >