Re: KVM: x86/xen: Allow 'out of range' event channel ports in IRQ routing table.

[David Woodhouse]

On Mon, 2025-05-12 at 10:29 +0100, Paul Durrant wrote:
> On 08/05/2025 21:30, David Woodhouse wrote:
> > From: David Woodhouse <dwmw@xxxxxxxxxxxx>
> > 
> > To avoid imposing an ordering constraint on userspace, allow 'invalid'
> > event channel targets to be configured in the IRQ routing table.
> > 
> > This is the same as accepting interrupts targeted at vCPUs which don't
> > exist yet, which is already the case for both Xen event channels *and*
> > for MSIs (which don't do any filtering of permitted APIC ID targets at
> > all).
> > 
> > If userspace actually *triggers* an IRQ with an invalid target, that
> > will fail cleanly, as kvm_xen_set_evtchn_fast() also does the same range
> > check.
> > 
> > If KVM enforced that the IRQ target must be valid at the time it is
> > *configured*, that would force userspace to create all vCPUs and do
> > various other parts of setup (in this case, setting the Xen long_mode)
> > before restoring the IRQ table.
> > 
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> > ---
> >   arch/x86/kvm/xen.c | 14 ++++++++++++--
> >   1 file changed, 12 insertions(+), 2 deletions(-)
> > 
> 
> Reviewed-by: Paul Durrant <paul@xxxxxxx>

Ping?

Attachment: smime.p7s
Description: S/MIME cryptographic signature