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SubjectRe: [PATCH v6 12/14] KVM: x86: Introduce KVM_PAGE_ENC_BITMAP_RESET ioctl
Hello Steve,

On Tue, Apr 07, 2020 at 06:25:51PM -0700, Steve Rutherford wrote:
> On Mon, Apr 6, 2020 at 11:53 AM Krish Sadhukhan
> <krish.sadhukhan@oracle.com> 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@amd.com>
> > >>>
> > >>> 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@amd.com>
> > >>> ---
> > >>> 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@oracle.com>
>
>
> 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.

The set ioctl is generally available/provided for the incoming VM to setup
the page encryption bitmap, this reset ioctl is meant for the source VM
as a simple interface to reset the whole page encryption bitmap.

Thanks,
Ashish

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