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Re: [PATCH v8 02/13] vpci: use per-domain PCI lock to protect vpci structure
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 20 Jul 2023 15:50:58 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
- Delivery-date: Thu, 20 Jul 2023 13:52:05 +0000
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On Thu, Jul 20, 2023 at 03:27:29PM +0200, Jan Beulich wrote:
> On 20.07.2023 13:20, Roger Pau Monné wrote:
> > On Thu, Jul 20, 2023 at 12:32:31AM +0000, Volodymyr Babchuk wrote:
> >> @@ -447,8 +476,16 @@ void vpci_write(pci_sbdf_t sbdf, unsigned int reg,
> >> unsigned int size,
> >>
> >> /*
> >> * Find the PCI dev matching the address, which for hwdom also
> >> requires
> >> - * consulting DomXEN. Passthrough everything that's not trapped.
> >> + * consulting DomXEN. Passthrough everything that's not trapped.
> >> + * If this is hwdom, we need to hold locks for both domain in case if
> >> + * modify_bars is called()
> >
> > Typo: the () wants to be at the end of modify_bars().
> >
> >> */
> >> + read_lock(&d->pci_lock);
> >> +
> >> + /* dom_xen->pci_lock always should be taken second to prevent
> >> deadlock */
> >> + if ( is_hardware_domain(d) )
> >> + read_lock(&dom_xen->pci_lock);
> >
> > For modify_bars() we also want the locks to be in write mode (at least
> > the hw one), so that the position of the BARs can't be changed while
> > modify_bars() is iterating over them.
>
> Isn't changing of the BARs happening under the vpci lock?
It is.
> Or else I guess
> I haven't understood the description correctly: My reading so far was
> that it is only the presence (allocation status / pointer validity) that
> is protected by this new lock.
Hm, I see, yes. I guess it was a previous patch version that also
took care of the modify_bars() issue by taking the lock in exclusive
mode here.
We can always do that later, so forget about that comment (for now).
Thanks, Roger.
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