Re: [RFC v2 PATCH 13/13] KVM: Enable memfd based page invalidation/fallocate

[Kirill A. Shutemov]

On Fri, Nov 19, 2021 at 09:47:39PM +0800, Chao Peng wrote:
> Since the memory backing store does not get notified when VM is
> destroyed so need check if VM is still live in these callbacks.
> 
> Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> ---
>  virt/kvm/memfd.c | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)
> 
> diff --git a/virt/kvm/memfd.c b/virt/kvm/memfd.c
> index bd930dcb455f..bcfdc685ce22 100644
> --- a/virt/kvm/memfd.c
> +++ b/virt/kvm/memfd.c
> @@ -12,16 +12,38 @@
>  #include <linux/memfd.h>
>  const static struct guest_mem_ops *memfd_ops;
>  
> +static bool vm_is_dead(struct kvm *vm)
> +{
> +	struct kvm *kvm;
> +
> +	list_for_each_entry(kvm, &vm_list, vm_list) {
> +		if (kvm == vm)
> +			return false;
> +	}

I don't think this is enough. The struct kvm can be freed and re-allocated
from the slab and this function will give false-negetive.

Maybe the kvm has to be tagged with a sequential id that incremented every
allocation. This id can be checked here.

> +
> +	return true;
> +}

-- 
 Kirill A. Shutemov