Re: [Xen-devel] [PATCH V3 2/2] Xen/PCIback: Implement PCI flr/slot/bus reset with 'reset' SysFS attribute

[Håkon Alstadheim <hakon@xxxxxxxxxxxxxxxxxx>]

Den 19.10.2020 13:00, skrev George Dunlap:
> > On Jan 31, 2020, at 3:33 PM, Wei Liu <wl@xxxxxxx> wrote:
> >
> > On Fri, Jan 17, 2020 at 02:13:04PM -0500, Rich Persaud wrote:
> > > On Aug 26, 2019, at 17:08, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
> > > > Hi,
> > > >
> > > > > On Mon, Oct 08, 2018 at 10:32:45AM -0400, Boris Ostrovsky wrote:
> > > > > > On 10/3/18 11:51 AM, Pasi Kärkkäinen wrote:
> > > > > > On Wed, Sep 19, 2018 at 11:05:26AM +0200, Roger Pau Monné wrote:
> > > > > > > On Tue, Sep 18, 2018 at 02:09:53PM -0400, Boris Ostrovsky wrote:
> > > > > > > > On 9/18/18 5:32 AM, George Dunlap wrote:
> > > > > > > > > > On Sep 18, 2018, at 8:15 AM, Pasi Kärkkäinen <pasik@xxxxxx> wrote:
> > > > > > > > > > Hi,
> > > > > > > > > > On Mon, Sep 17, 2018 at 02:06:02PM -0400, Boris Ostrovsky wrote:
> > > > > > > > > > > What about the toolstack changes? Have they been accepted? I vaguely
> > > > > > > > > > > recall there was a discussion about those changes but don't remember how
> > > > > > > > > > > it ended.
> > > > > > > > > > I don't think toolstack/libxl patch has been applied yet either.
> > > > > > > > > > "[PATCH V1 0/1] Xen/Tools: PCI reset using 'reset' SysFS attribute":
> > > > > > > > > > https://lists.xen.org/archives/html/xen-devel/2017-12/msg00664.html
> > > > > > > > > > "[PATCH V1 1/1] Xen/libxl: Perform PCI reset using 'reset' SysFS attribute":
> > > > > > > > > > https://lists.xen.org/archives/html/xen-devel/2017-12/msg00663.html
> > > > > > > > Will this patch work for *BSD? Roger?
> > > > > > > At least FreeBSD don't support pci-passthrough, so none of this works
> > > > > > > ATM. There's no sysfs on BSD, so much of what's in libxl_pci.c will
> > > > > > > have to be moved to libxl_linux.c when BSD support is added.
> > > > > > Ok. That sounds like it's OK for the initial pci 'reset' implementation in 
> > > > > > xl/libxl to be linux-only..
> > > > > Are these two patches still needed? ISTR they were  written originally
> > > > > to deal with guest trying to use device that was previously assigned to
> > > > > another guest. But pcistub_put_pci_dev() calls
> > > > > __pci_reset_function_locked() which first tries FLR, and it looks like
> > > > > it was added relatively recently.
> > > > Replying to an old thread.. I only now realized I forgot to reply to this 
> > > > message earlier.
> > > >
> > > > afaik these patches are still needed. Håkon (CC'd) wrote to me in private that
> > > > he gets a (dom0) Linux kernel crash if he doesn't have these patches applied.
> > > >
> > > >
> > > > Here are the links to both the linux kernel and libxl patches:
> > > >
> > > >
> > > > "[Xen-devel] [PATCH V3 0/2] Xen/PCIback: PCI reset using 'reset' SysFS 
> > > > attribute":
> > > > https://lists.xen.org/archives/html/xen-devel/2017-12/msg00659.html
> > > >
> > > > [Note that PATCH V3 1/2 "Drivers/PCI: Export pcie_has_flr() interface" is 
> > > > already applied in upstream linux kernel, so it's not needed anymore]
> > > >
> > > > "[Xen-devel] [PATCH V3 2/2] Xen/PCIback: Implement PCI flr/slot/bus reset with 
> > > > 'reset' SysFS attribute":
> > > > https://lists.xen.org/archives/html/xen-devel/2017-12/msg00661.html
> > > >
> > > >
> > > > "[Xen-devel] [PATCH V1 0/1] Xen/Tools: PCI reset using 'reset' SysFS attribute":
> > > > https://lists.xen.org/archives/html/xen-devel/2017-12/msg00664.html
> > > >
> > > > "[Xen-devel] [PATCH V1 1/1] Xen/libxl: Perform PCI reset using 'reset' SysFS 
> > > > attribute":
> > > > https://lists.xen.org/archives/html/xen-devel/2017-12/msg00663.html
> > > [dropping Linux mailing lists]
> > >
> > > What is required to get the Xen patches merged?  Rebasing against Xen
> > > master?  OpenXT has been carrying a similar patch for many years and
> > > we would like to move to an upstream implementation.  Xen users of PCI
> > > passthrough would benefit from more reliable device reset.
> > Rebase and resend?
> >
> > Skimming that thread I think the major concern was backward
> > compatibility. That seemed to have been addressed.
> >
> > Unfortunately I don't have the time to dig into Linux to see if the
> > claim there is true or not.
> >
> > It would be helpful to write a concise paragraph to say why backward
> > compatibility is not required.
> Just going through my old “make sure something happens with this” mails.  Did 
> anything ever happen with this?  Who has the ball here / who is this stuck on?
We're waiting for "somebody" to testify that fixing this will not 
adversely affect anyone. I'm not qualified, but my strong belief is that 
since "reset" or "do_flr"  in the linux kernel is not currently 
implemented/used in any official distribution, it should be OK.
Patches still work in current staging-4.14 btw.