linux-kernel - Re: [PATCH] xen: issue warning message when out of grant maptrack entries

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Date:   Tue, 18 Sep 2018 13:03:14 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] xen: issue warning message when out of grant maptrack
 entries

On 9/18/18 5:32 AM, Juergen Gross wrote:
> When a driver domain (e.g. dom0) is running out of maptrack entries it
> can't map any more foreign domain pages. Instead of silently stalling
> the affected domUs issue a rate limited warning in this case in order
> to make it easier to detect that situation.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  drivers/xen/grant-table.c | 25 +++++++++++++++++++------
>  1 file changed, 19 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c
> index 7bafa703a992..09f6ff8c1957 100644
> --- a/drivers/xen/grant-table.c
> +++ b/drivers/xen/grant-table.c
> @@ -1040,18 +1040,31 @@ int gnttab_map_refs(struct gnttab_map_grant_ref *map_ops,
>  		return ret;
>  
>  	for (i = 0; i < count; i++) {
> -		/* Retry eagain maps */
> -		if (map_ops[i].status == GNTST_eagain)
> -			gnttab_retry_eagain_gop(GNTTABOP_map_grant_ref, map_ops + i,
> -						&map_ops[i].status, __func__);
> -
> -		if (map_ops[i].status == GNTST_okay) {
> +		switch (map_ops[i].status) {
> +		case GNTST_okay:
> +		{
>  			struct xen_page_foreign *foreign;
>  
>  			SetPageForeign(pages[i]);
>  			foreign = xen_page_foreign(pages[i]);
>  			foreign->domid = map_ops[i].dom;
>  			foreign->gref = map_ops[i].ref;
> +			break;
> +		}
> +
> +		case GNTST_no_device_space:
> +			pr_warn_ratelimited("maptrack limit reached, can't map all guest pages\n");
> +			break;
> +
> +		case GNTST_eagain:
> +			/* Retry eagain maps */
> +			gnttab_retry_eagain_gop(GNTTABOP_map_grant_ref,
> +						map_ops + i,
> +						&map_ops[i].status, __func__);
> +			break;
> +
> +		default:
> +			break;
>  		}
>  	}


Should we pass 'i' instead of count to set_foreign_p2m_mapping() below?
The loop there will skip entries that are in error, but does it make
sense to do the hypercall for kmap_ops with count>i ?

-boris