Re: [PATCH 2/2] KVM: Prevent internal slots from being COWed

[Marcelo Tosatti <mtosatti@redhat.com>]

On Mon, Jun 21, 2010 at 11:18:13AM +0300, Avi Kivity wrote:
> If a process with a memory slot is COWed, the page will change its address
> (despite having an elevated reference count).  This breaks internal memory
> slots which have their physical addresses loaded into vmcs registers (see
> the APIC access memory slot).
> 
> Signed-off-by: Avi Kivity <avi@redhat.com>
> ---
>  arch/x86/kvm/x86.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 33156a3..d9a33e6 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5633,6 +5633,11 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
>  				int user_alloc)
>  {
>  	int npages = memslot->npages;
> +	int map_flags = MAP_PRIVATE | MAP_ANONYMOUS;
> +
> +	/* Prevent internal slot pages from being moved by fork()/COW. */
> +	if (memslot->id >= KVM_MEMORY_SLOTS)
> +		map_flags = MAP_SHARED | MAP_ANONYMOUS;
>  
>  	/*To keep backward compatibility with older userspace,
>  	 *x86 needs to hanlde !user_alloc case.

Forgot to use map_flags below.