On 2024/2/21 1:15, Oliver Upton wrote:
Hi Zenghui,
On Wed, Feb 21, 2024 at 12:30:24AM +0800, Zenghui Yu wrote:
On 2024/2/17 02:41, Oliver Upton wrote:
Using a linked-list for LPIs is less than ideal as it of course requires
iterative searches to find a particular entry. An xarray is a better
data structure for this use case, as it provides faster searches and can
still handle a potentially sparse range of INTID allocations.
Start by storing LPIs in an xarray, punting usage of the xarray to a
subsequent change.
Signed-off-by: Oliver Upton <oliver.upton@xxxxxxxxx>
[..]
diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
index db2a95762b1b..c126014f8395 100644
--- a/arch/arm64/kvm/vgic/vgic.c
+++ b/arch/arm64/kvm/vgic/vgic.c
@@ -131,6 +131,7 @@ void __vgic_put_lpi_locked(struct kvm *kvm, struct vgic_irq *irq)
return;
list_del(&irq->lpi_list);
+ xa_erase(&dist->lpi_xa, irq->intid);
We can get here *after* grabbing the vgic_cpu->ap_list_lock (e.g.,
vgic_flush_pending_lpis()/vgic_put_irq()). And as according to vGIC's
"Locking order", we should disable interrupts before taking the xa_lock
in xa_erase() and we would otherwise see bad things like deadlock..
Nice catch!
Yeah, the general intention was to disable interrupts outside of the
xa_lock, however:
It's not a problem before patch #10, where we drop the lpi_list_lock and
start taking the xa_lock with interrupts enabled. Consider switching to
use xa_erase_irq() instead?
I don't think this change is safe until #10, as the implied xa_unlock_irq()
would re-enable interrupts before the lpi_list_lock is dropped. Or do I
have wires crossed?
No, you're right. My intention was to fix it in patch #10. And as
you've both pointed out, using xa_erase_irq() can hardly be the correct
fix. My mistake :-( .
Thanks,
Zenghui
