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KVM: arm64: vgic-v4: Fall back to software irqbypass if LPI not found

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Continuing with the theme of broken VMMs and guests, irqbypass
registration can fail if the virtual ITS lacks a translation for the
MSI. Either the guest hasn't mapped it or userspace may have forgotten
to restore the ITS.

Exit silently and allow irqbypass configuration to succeed. As a reward
for ingenuity, LPIs are demoted to software injection.

Tested-by: Sudheer Dantuluri <dantuluris@google.com>
Fixes: 196b136498 ("KVM: arm/arm64: GICv4: Wire mapping/unmapping of VLPIs in VFIO irq bypass")
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20250226183124.82094-4-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
This commit is contained in:
Oliver Upton 2025-02-26 10:31:23 -08:00
parent d0b79563fd
commit 5c57533eb8
1 changed files with 10 additions and 5 deletions
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15
arch/arm64/kvm/vgic/vgic-v4.c
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@ -415,7 +415,7 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq,
struct vgic_irq *irq;
struct its_vlpi_map map;
unsigned long flags;
int ret;
int ret = 0;
if (!vgic_supports_direct_msis(kvm))
return 0;
@ -430,10 +430,15 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, int virq,
mutex_lock(&its->its_lock);
/* Perform the actual DevID/EventID -> LPI translation. */
ret = vgic_its_resolve_lpi(kvm, its, irq_entry->msi.devid,
irq_entry->msi.data, &irq);
if (ret)
/*
* Perform the actual DevID/EventID -> LPI translation.
*
* Silently exit if translation fails as the guest (or userspace!) has
* managed to do something stupid. Emulated LPI injection will still
* work if the guest figures itself out at a later time.
*/
if (vgic_its_resolve_lpi(kvm, its, irq_entry->msi.devid,
irq_entry->msi.data, &irq))
goto out;
/* Silently exit if the vLPI is already mapped */