On Thu, Jul 23, 2009 at 04:59:38PM -0300, Marcelo Tosatti wrote:
> On Wed, Jul 22, 2009 at 05:41:22PM +0300, Michael S. Tsirkin wrote:
> > Kernels up to 2.6.31 have a bug: MSI entries where looked at when irq
> > is acked, address_lo was interpreted as irqchip, and
> > address_hi as pin. If that matches a real interrupt this prevents
> > ack notifier from being processed.
> >
> > Since these kernels ignore the value for address_hi when delivering
> > MSI, work around this by setting a value that never matches an
> > interrupt pin number.
> >
> > Pointers to relevant kernel code, for reference: in kernel v2.6.31-rc3:
> > kvm_notify_acked_irq - fails to check irq type,
> > kvm_set_msi - ignored address_hi in message
>
> Ugh, its still broken AFAICS? If so, what is the plan to fix it?
>
I'd like Avi's input on that.
One can imagine multiple ways to fix this in kernel. One possible way
proposed by Gleb recently is switching to a new send_msi ioctl.
If we do it this way, we can just keep the old interface as broken.
> Also, you'd never want to use address_hi for something, in the
> future?
AFAIK apic always has 0 in address_hi. Maybe x2apic is different, we can
deactivate the workaround in userspace if we ever enable x2apic.
> > Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> > ---
> > qemu-kvm.c | 32 ++++++++++++++++++++++++++++++--
> > 1 files changed, 30 insertions(+), 2 deletions(-)
> >
> > diff --git a/qemu-kvm.c b/qemu-kvm.c
> > index cebaa65..ec6d583 100644
> > --- a/qemu-kvm.c
> > +++ b/qemu-kvm.c
> > @@ -38,6 +38,32 @@
> > #error libkvm: userspace and kernel version mismatch
> > #endif
> >
> > +#ifdef KVM_CAP_IRQ_ROUTING
> > +/* Broken MSI routing work-around:
> > + * Kernels up to 2.6.31 have a bug: MSI entries where looked at when irq
> > + * is acked, address_lo was interpreted as irqchip, and
> > + * address_hi as pin. If that matches a real interrupt this prevents
> > + * ack notifier from being processed.
> > + *
> > + * Since these kernels ignore the value for address_hi when delivering
> > + * MSI, work around this by setting a value that never matches an
> > + * interrupt pin number.
> > + */
> > +#define KVM_BROKEN_MSI_ROUTING 1
> > +static inline
> > +void kvm_broken_msi_fix(struct kvm_irq_routing_entry *entry)
> > +{
> > + if (entry->type == KVM_IRQ_ROUTING_MSI) {
> > + entry->u.msi.address_hi = 0xffffffff;
> > + }
> > +}
> > +static inline
> > +unsigned kvm_broken_msi_address_hi(struct kvm_irq_routing_entry *entry)
> > +{
> > + return 0xffffffff;
> > +}
> > +#endif
> > +
> > int kvm_allowed = 1;
> > int kvm_irqchip = 1;
> > int kvm_pit = 1;
> > @@ -1433,6 +1459,7 @@ int kvm_add_routing_entry(kvm_context_t kvm,
> > new->type = entry->type;
> > new->flags = entry->flags;
> > new->u = entry->u;
> > + kvm_broken_msi_fix(new);
> >
> > set_gsi(kvm, entry->gsi);
> >
> > @@ -1489,7 +1516,7 @@ int kvm_del_routing_entry(kvm_context_t kvm,
> > if (e->u.msi.address_lo ==
> > entry->u.msi.address_lo
> > && e->u.msi.address_hi ==
> > - entry->u.msi.address_hi
> > + kvm_broken_msi_address_hi(entry)
> > && e->u.msi.data == entry->u.msi.data) {
> > p = &kvm->irq_routes->
> > entries[--kvm->irq_routes->nr];
> > @@ -1550,9 +1577,10 @@ int kvm_update_routing_entry(kvm_context_t kvm,
> > break;
> > case KVM_IRQ_ROUTING_MSI:
> > if (e->u.msi.address_lo == entry->u.msi.address_lo &&
> > - e->u.msi.address_hi == entry->u.msi.address_hi &&
> > + e->u.msi.address_hi == kvm_broken_msi_address_hi(entry) &&
> > e->u.msi.data == entry->u.msi.data) {
> > memcpy(&e->u.msi, &newentry->u.msi, sizeof e->u.msi);
> > + kvm_broken_msi_fix(e);
> > return 0;
> > }
> > break;
> > --
> > 1.6.2.5
> > --
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