Re: [PATCH v3 1/2] vfio: move the function vfio_get_xlat_addr() to memory.c

[Alex Williamson]

On Wed, 26 Oct 2022 00:37:33 +0800
Cindy Lu <lulu@redhat.com> wrote:
> diff --git a/softmmu/memory.c b/softmmu/memory.c
> index 7ba2048836..03940c551d 100644
> --- a/softmmu/memory.c
> +++ b/softmmu/memory.c
...
> +        /*
> +         * Malicious VMs might trigger discarding of IOMMU-mapped memory. The
> +         * pages will remain pinned inside vfio until unmapped, resulting in 
> a
> +         * higher memory consumption than expected. If memory would get
> +         * populated again later, there would be an inconsistency between 
> pages
> +         * pinned by vfio and pages seen by QEMU. This is the case until
> +         * unmapped from the IOMMU (e.g., during device reset).
> +         *
> +         * With malicious guests, we really only care about pinning more 
> memory
> +         * than expected. RLIMIT_MEMLOCK set for the user/process can never 
> be
> +         * exceeded and can be used to mitigate this problem.
> +         */
> +        warn_report_once("Using vfio with vIOMMUs and coordinated discarding 
> of"
> +                         " RAM (e.g., virtio-mem) works, however, malicious"
> +                         " guests can trigger pinning of more memory than"
> +                         " intended via an IOMMU. It's possible to mitigate "
> +                         " by setting/adjusting RLIMIT_MEMLOCK.");

Looks like the comment and warning still need to be generalized for
shared use here.  Thanks,

Alex