Re: "swiotlb buffer is full" in DomU with PCI passthrough is caused by low memory in Dom0

[Paul Leiber <paul@xxxxxxxxxxxxxxxx>]

Am 28.04.2023 um 17:28 schrieb zithro:
> On 25 Apr 2023 22:30, Paul Leiber wrote:
> > Hi,
> Hi,
>
> > I can't rule out that there actually is a log entry in Dom0 for this 
> > situation, and my Xen and/or linux knowledge was not good enough to 
> > let me find it. If this is the case, I'd appreciate some pointers.
> Then why not posting your logs ?
I didn't find anything that seemed relevant, that's why I didn't post 
any logs. Also, I am not sure which logs are relevant (see below).
As this is from a "production" machine (the family internet connection 
gateway at home), I need to literally beg for time windows where I can 
do the testing, hence I am hesitant to promise any logs soon.
That put aside: Which logs would be relevant? The ones below, or 
more/others?
> Did you add "loglvl=all" and/or "guest_loglvl=all" to Xen cmdline ?
Yes.

> What logs did you read: "dmesg", "xl dmesg" or logs in /var/log/xen ?
I looked at the logs in /var/log/xen and dmesg, don't remember if a also 
looked at "xl dmesg".
>  From the (few) posts I've read, this problems happens on 
> non-virtualized systems, so maybe it's not related to Xen at all.
> Maybe it's a driver problem.
> (Search query used: "swiotlb buffer is full").
I also noticed that most reports of swiotlib issues are for 
non-virtualized systems. But: If my reported issue was not Xen related, 
why would changing the amount of Dom0 memory influence DomU behavior?
> Also I found pointers related to the *domU* kernel command line option 
> "swiotlb", like using "swiotlb=1" or "swiotlb=65536"
Interesting, thank you for the hint.

> PS: I'm not an expert, just a Xen user ;)
Same, although I still consider myself a Xen beginner. :-)