Re: [PATCH v2 1/2] xen: don't allow gnttab_dma_[alloc|free]_pages() in PV guest

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

On 10/11/2026 9:56 am, Juergen Gross wrote:
> Today gnttab_dma_alloc_pages() or gnttab_dma_free_pages are never
> called when running as a PV guest, but this holds for in-tree callers
> only.
>
> Bail out early when being called in PV mode in order to ensure no out
> of tree module or future use cases are violating this assumption.
>
> This enables to safely remove PV-only code from both functions.
>
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
>  drivers/xen/grant-table.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index 604c4eea5930..56a497987942 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -1063,6 +1063,9 @@ int gnttab_dma_alloc_pages(struct gnttab_dma_alloc_args *args)
>  	size_t size;
>  	int i, ret;
>  
> +	if (WARN_ON(xen_pv_domain()))
> +		return -EINVAL;

This will get very spammy if hit.  WARN_ON_ONCE() ?

~Andrew