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SubjectRe: [PATCH] xen: issue warning message when out of grant maptrack entries
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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@suse.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?

-boris


>>
>> 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 ?
> The loop is running until the end, so i == count for the call of kmap_ops().
>
>
> Juergen

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