Re: [PATCH v8 08/13] confidential guest support: Move SEV initialization into arch specific code

[Greg Kurz]

On Tue,  2 Feb 2021 15:13:10 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> While we've abstracted some (potential) differences between mechanisms for
> securing guest memory, the initialization is still specific to SEV.  Given
> that, move it into x86's kvm_arch_init() code, rather than the generic
> kvm_init() code.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> Reviewed-by: Cornelia Huck <cohuck@redhat.com>
> ---

Reviewed-by: Greg Kurz <groug@kaod.org>

>  accel/kvm/kvm-all.c   | 14 --------------
>  accel/kvm/sev-stub.c  |  4 ++--
>  target/i386/kvm/kvm.c | 20 ++++++++++++++++++++
>  target/i386/sev.c     |  7 ++++++-
>  4 files changed, 28 insertions(+), 17 deletions(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 3d820d0c7d..7150acdbcc 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -2180,20 +2180,6 @@ static int kvm_init(MachineState *ms)
>  
>      kvm_state = s;
>  
> -    /*
> -     * if memory encryption object is specified then initialize the memory
> -     * encryption context.
> -     */
> -    if (ms->cgs) {
> -        Error *local_err = NULL;
> -        /* FIXME handle mechanisms other than SEV */
> -        ret = sev_kvm_init(ms->cgs, &local_err);
> -        if (ret < 0) {
> -            error_report_err(local_err);
> -            goto err;
> -        }
> -    }
> -
>      ret = kvm_arch_init(ms, s);
>      if (ret < 0) {
>          goto err;
> diff --git a/accel/kvm/sev-stub.c b/accel/kvm/sev-stub.c
> index 512e205f7f..9587d1b2a3 100644
> --- a/accel/kvm/sev-stub.c
> +++ b/accel/kvm/sev-stub.c
> @@ -17,6 +17,6 @@
>  
>  int sev_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
>  {
> -    /* SEV can't be selected if it's not compiled */
> -    g_assert_not_reached();
> +    /* If we get here, cgs must be some non-SEV thing */
> +    return 0;
>  }
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index 6dc1ee052d..4788139128 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -42,6 +42,7 @@
>  #include "hw/i386/intel_iommu.h"
>  #include "hw/i386/x86-iommu.h"
>  #include "hw/i386/e820_memory_layout.h"
> +#include "sysemu/sev.h"
>  
>  #include "hw/pci/pci.h"
>  #include "hw/pci/msi.h"
> @@ -2135,6 +2136,25 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>      uint64_t shadow_mem;
>      int ret;
>      struct utsname utsname;
> +    Error *local_err = NULL;
> +
> +    /*
> +     * Initialize SEV context, if required
> +     *
> +     * If no memory encryption is requested (ms->cgs == NULL) this is
> +     * a no-op.
> +     *
> +     * It's also a no-op if a non-SEV confidential guest support
> +     * mechanism is selected.  SEV is the only mechanism available to
> +     * select on x86 at present, so this doesn't arise, but if new
> +     * mechanisms are supported in future (e.g. TDX), they'll need
> +     * their own initialization either here or elsewhere.
> +     */
> +    ret = sev_kvm_init(ms->cgs, &local_err);
> +    if (ret < 0) {
> +        error_report_err(local_err);
> +        return ret;
> +    }
>  
>      if (!kvm_check_extension(s, KVM_CAP_IRQ_ROUTING)) {
>          error_report("kvm: KVM_CAP_IRQ_ROUTING not supported by KVM");
> diff --git a/target/i386/sev.c b/target/i386/sev.c
> index f9e9b5d8ae..11c9a3cc21 100644
> --- a/target/i386/sev.c
> +++ b/target/i386/sev.c
> @@ -664,13 +664,18 @@ sev_vm_state_change(void *opaque, int running, RunState 
> state)
>  
>  int sev_kvm_init(ConfidentialGuestSupport *cgs, Error **errp)
>  {
> -    SevGuestState *sev = SEV_GUEST(cgs);
> +    SevGuestState *sev
> +        = (SevGuestState *)object_dynamic_cast(OBJECT(cgs), TYPE_SEV_GUEST);
>      char *devname;
>      int ret, fw_error;
>      uint32_t ebx;
>      uint32_t host_cbitpos;
>      struct sev_user_data_status status = {};
>  
> +    if (!sev) {
> +        return 0;
> +    }
> +
>      ret = ram_block_discard_disable(true);
>      if (ret) {
>          error_report("%s: cannot disable RAM discard", __func__);