Re: [PATCH 3/3] domctl: pause vCPU for context reads

[Andrew Cooper <andrew.cooper3@citrix.com>]

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On 05/02/14 14:54, Jan Beulich wrote:
> "Base" context reads already paused the subject vCPU when being the
> current one, but that special case isn't being properly dealt with
> anyway (at the very least when x86's fsgsbase feature is in use), so
> just disallow it.
>
> "Extended" context reads so far didn't do any pausing.
>
> While we can't avoid the reported data being stale by the time it
> arrives at the caller, this way we at least guarantee that it is
> consistent.
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Now I come to think about it, is this an ABI change, as we are now
disallowing a control domain to issue these hypercalls on itself?

~Andrew

>
> --- a/xen/arch/x86/domctl.c
> +++ b/xen/arch/x86/domctl.c
> @@ -819,7 +819,13 @@ long arch_do_domctl(
>  
>          if ( domctl->cmd == XEN_DOMCTL_get_ext_vcpucontext )
>          {
> +            if ( v == current ) /* no vcpu_pause() */
> +                break;
> +
>              evc->size = sizeof(*evc);
> +
> +            vcpu_pause(v);
> +
>              if ( is_pv_domain(d) )
>              {
>                  evc->sysenter_callback_cs      =
> @@ -849,6 +855,7 @@ long arch_do_domctl(
>              evc->vmce.mci_ctl2_bank1 = v->arch.vmce.bank[1].mci_ctl2;
>  
>              ret = 0;
> +            vcpu_unpause(v);
>              copyback = 1;
>          }
>          else
> --- a/xen/common/domctl.c
> +++ b/xen/common/domctl.c
> @@ -675,11 +675,9 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
>          struct vcpu         *v;
>  
>          ret = -EINVAL;
> -        if ( op->u.vcpucontext.vcpu >= d->max_vcpus )
> -            goto getvcpucontext_out;
> -
> -        ret = -ESRCH;
> -        if ( (v = d->vcpu[op->u.vcpucontext.vcpu]) == NULL )
> +        if ( op->u.vcpucontext.vcpu >= d->max_vcpus ||
> +             (v = d->vcpu[op->u.vcpucontext.vcpu]) == NULL ||
> +             v == current ) /* no vcpu_pause() */
>              goto getvcpucontext_out;
>  
>          ret = -ENODATA;
> @@ -694,14 +692,12 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
>          if ( (c.nat = xmalloc(struct vcpu_guest_context)) == NULL )
>              goto getvcpucontext_out;
>  
> -        if ( v != current )
> -            vcpu_pause(v);
> +        vcpu_pause(v);
>  
>          arch_get_info_guest(v, c);
>          ret = 0;
>  
> -        if ( v != current )
> -            vcpu_unpause(v);
> +        vcpu_unpause(v);
>  
>  #ifdef CONFIG_COMPAT
>          if ( !is_pv_32on64_vcpu(v) )
>
>
>
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xen.org
> http://lists.xen.org/xen-devel


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