xen-devel
Re: [Xen-devel] Re: [PATCH 09/22] xen: Find an unbound irq number in rev
On Thu, Oct 07, 2010 at 11:38:49AM +0100, Stefano Stabellini wrote:
> On Wed, 6 Oct 2010, Konrad Rzeszutek Wilk wrote:
> > >
> > > Unfortunately this is the wrong way to fix the issue: Xen has a range of
> > > allowed pirq for each domain and we don't know exactly what is the
> > > maximum pirq (see my patch "xen: get the maximum number of pirqs from
> > > xen" [1]).
> >
> > > Considering that we might use the irq number returned by
> > > find_unbound_irq through xen_allocate_pirq as pirq number in some cases,
> >
> > Ah, but we wouldn't! We would end up only using the 'find_unbound_irq' for
> > event channels. For IRQs that are for physical devices (either being
> > real devices passed in or QEMU PCI devices) we end up requesting an IRQ that
> > matches whatever the device has defined in dev->irq (or whatever the
> > vectors values for MSI/MSI-X devices that is provided) via the Xen PCI
> > frontend
> > driver (in case of QEMU whatever its emulation provides).
> >
> > > starting from the highest value could be unsafe.
> > > In practice it should be impossible to see this issue because it can
> > > only happen if the irq returned by xen_allocate_pirq is higher than the
> > > max pirq in xen. However AFAIK when we call xen_allocate_pirq with the
> > > intention of using the return value as pirq we always fall in the if
> > > (identity_mapped_irq(gsi) || !xen_initial_domain()) that avoid calling
> > > find_unbound_irq.
> >
> > Right, and we end up using an the pirq/gsi number at that point. This
> > patch would not touch that logic.
>
> What about adding a comment on top of xen_allocate_pirq like the
> following:
>
> /* xen_allocate_irq might allocate irqs from the top down, as a
> * consequence don't assume that the irq number returned has a low value
> * or can be used as a pirq number unless you know otherwise.
> *
> * One notable exception is when xen_allocate_irq is called passing an
> * hardware gsi as argument, in that case the irq number returned
> * matches the gsi number passed as first argument.
> */
Done!
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- [Xen-devel] [PATCH 01/22] xen: Don't disable the I/O space, (continued)
- [Xen-devel] [PATCH 01/22] xen: Don't disable the I/O space, Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 14/22] x86/PCI: Export pci_walk_bus function., Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 03/22] xen: implement pirq type event channels, Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 22/22] MAINTAINERS: Add myself for Xen PCI and Xen SWIOTLB maintainer., Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 13/22] x86/PCI: make sure _PAGE_IOMAP it set on pci mappings, Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 21/22] xen/pci: Request ACS when Xen-SWIOTLB is activated., Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 09/22] xen: Find an unbound irq number in reverse order (high to low)., Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 07/22] xen: set pirq name to something useful., Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 02/22] xen: define BIOVEC_PHYS_MERGEABLE(), Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 15/22] x86: Copy-n-paste arch_teardown_msi_irqs from msi.c to io_apic.c., Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 16/22] x86: Introduce x86_msi_ops, Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 08/22] xen: statically initialize cpu_evtchn_mask_p, Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 12/22] x86/PCI: Clean up pci_cache_line_size, Konrad Rzeszutek Wilk
- [Xen-devel] [PATCH 05/22] xen: identity map gsi->irqs, Konrad Rzeszutek Wilk
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