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From: Jan Beulich <jbeulich@suse.com>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>,
	Konrad Wilk <konrad.wilk@oracle.com>,
	"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH 1/3] xen-pciback: redo VF placement in the virtual topology
Date: Fri, 9 Apr 2021 10:16:31 +0200	[thread overview]
Message-ID: <4e39de85-1b03-0fb4-805a-69a16bbaafa6@suse.com> (raw)
In-Reply-To: <b41663ff-6a90-877d-9cd3-7e052c28eb6a@oracle.com>

On 09.04.2021 00:28, Boris Ostrovsky wrote:
> 
> On 4/7/21 10:37 AM, Jan Beulich wrote:
>> The commit referenced below was incomplete: It merely affected what
>> would get written to the vdev-<N> xenstore node. The guest would still
>> find the function at the original function number as long as 
>> __xen_pcibk_get_pci_dev() wouldn't be in sync. The same goes for AER wrt
>> __xen_pcibk_get_pcifront_dev().
>>
>> Undo overriding the function to zero and instead make sure that VFs at
>> function zero remain alone in their slot. This has the added benefit of
>> improving overall capacity, considering that there's only a total of 32
>> slots available right now (PCI segment and bus can both only ever be
>> zero at present).
>>
>> Fixes: 8a5248fe10b1 ("xen PV passthru: assign SR-IOV virtual functions to separate virtual slots")
>> Signed-off-by: Jan Beulich <jbeulich@suse.com>
>> Cc: stable@vger.kernel.org
>> ---
>> Like the original change this has the effect of changing where devices
>> would appear in the guest, when there are multiple of them. I don't see
>> an immediate problem with this, but if there is we may need to reduce
>> the effect of the change.
>> Taking into account, besides the described breakage, how xen-pcifront's
>> pcifront_scan_bus() works, I also wonder what problem it was in the
>> first place that needed fixing. It may therefore also be worth to
>> consider simply reverting the original change.
> 
> 
> Perhaps this is no longer a problem, it's been 9 years since that patch. Have you tried reverting to 8a5248fe10b101104d92d01438f918e899414fd1~1 and testing that?

Well, no, for the simple reason that I don't really understand how that
change was meant to make a difference. Hence while simply reverting may
be an option, it's not something I would want to suggest myself (simply
because I couldn't fully justify doing so).

Jan


  reply	other threads:[~2021-04-09  8:16 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-07 14:35 [PATCH 0/3] xen-pciback: a fix, a workaround, and some simplification Jan Beulich
2021-04-07 14:37 ` [PATCH 1/3] xen-pciback: redo VF placement in the virtual topology Jan Beulich
2021-04-08 22:28   ` Boris Ostrovsky
2021-04-09  8:16     ` Jan Beulich [this message]
2021-04-07 14:37 ` [PATCH 2/3] xen-pciback: reconfigure also from backend watch handler Jan Beulich
2021-04-09 21:43   ` Boris Ostrovsky
2021-04-12  9:44     ` Jan Beulich
2021-04-12 15:55       ` Boris Ostrovsky
2021-04-07 14:37 ` [PATCH 3/3] xen-pciback: simplify vpci's find hook Jan Beulich
2021-04-09 21:45   ` Boris Ostrovsky
2021-04-12  9:50     ` Jan Beulich
2021-04-12 16:05       ` Boris Ostrovsky
2021-04-13  8:09         ` Jan Beulich
2021-04-13 12:54           ` Boris Ostrovsky
2021-04-23  8:05   ` Juergen Gross

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