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

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Date:   Wed, 19 Sep 2018 15:34:15 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.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 19/09/18 15:29, Boris Ostrovsky wrote:
> On 9/18/18 1:17 PM, Juergen Gross wrote:
>> On 18/09/18 19:03, Boris Ostrovsky wrote:
>>> 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;
>>>>  		}
>>>>  	}
> 
> 
> After having a second look at this (and at the risk of embarrassing
> myself again with this patch) --- aren't we supposed to test status
> after gnttab_retry_eagain_gop() call, and then actually set foreign
> properties?

Right. Thanks for catching that!

V2 coming soon...


Juergen