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

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
>

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