Re: [PATCH v2 1/4] swiotlb-xen: ensure to issue well-formed XENMEM_exchange requests

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Fri, 17 Sep 2021, Jan Beulich wrote:
> While the hypervisor hasn't been enforcing this, we would still better
> avoid issuing requests with GFNs not aligned to the requested order.
> Instead of altering the value also in the call to panic(), drop it
> there for being static and hence easy to determine without being part
> of the panic message.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> I question how useful it is to wrap "bytes" in PAGE_ALIGN(), when it is
> a multiple of a segment's size anyway (or at least was supposed to be,
> prior to "swiotlb-xen: maintain slab count properly"). But that's
> perhaps yet another separate patch.
> ---
> v2: Drop logging of alignment. Wrap lines.
> 
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -230,10 +230,11 @@ retry:
>       /*
>        * Get IO TLB memory from any location.
>        */
> -     start = memblock_alloc(PAGE_ALIGN(bytes), PAGE_SIZE);
> +     start = memblock_alloc(PAGE_ALIGN(bytes),
> +                            IO_TLB_SEGSIZE << IO_TLB_SHIFT);
>       if (!start)
> -             panic("%s: Failed to allocate %lu bytes align=0x%lx\n",
> -                   __func__, PAGE_ALIGN(bytes), PAGE_SIZE);
> +             panic("%s: Failed to allocate %lu bytes\n",
> +                   __func__, PAGE_ALIGN(bytes));
>  
>       /*
>        * And replace that memory with pages under 4GB.
>