Re: [PATCH v3] VMX: don't crash processing 'd' debug key

[Keir Fraser <keir.xen@gmail.com>]

On 11/11/2013 12:55, "Jan Beulich" <JBeulich@suse.com> wrote:

> There's a window during scheduling where "current" and the active VMCS
> may disagree: The former gets set much earlier than the latter. Since
> both vmx_vmcs_enter() and vmx_vmcs_exit() immediately return when the
> subject vCPU is "current", accessing VMCS fields would, depending on
> whether there is any currently active VMCS, either read wrong data, or
> cause a crash.
> 
> Going forward we might want to consider reducing the window during
> which vmx_vmcs_enter() might fail (e.g. doing a plain __vmptrld() when
> v->arch.hvm_vmx.vmcs != this_cpu(current_vmcs) but arch_vmx->active_cpu
> == -1), but that would add complexities (acquiring and - more
> importantly - properly dropping v->arch.hvm_vmx.vmcs_lock) that don't
> look worthwhile adding right now.
> 
> Signed-off-by: Jan Beulich <jbeulich@suse.com>
> Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

This is a little ugly but I can't think of a nicer way.

Acked-by: Keir Fraser <keir@xen.org>