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DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org Mitigate a potential failure when inserting a new LPI into the VGIC LPI xarray. When vgic_add_lpi() is preparing to register a new LPI, it pre-allocates an xarray entry using xa_reserve_irq(), so that it can later perform the insertion under the xarray lock without allocating. However, since xa_reserve_irq() is called before acquiring such lock, there is a potential race where xa_reserve_irq() observes a populated entry, thus not performing the allocation, and another CPU removes that entry before the xarray lock is grabbed to perform the insertion. CPU0 (Adding new LPI) CPU1 (Releasing LPI) ===================== =================== vgic_add_lpi() /* Entry populated, does not allocate */ xa_reserve_irq(.., intid, ..) vgic_release_deleted_lpis() xa_lock_irqsave() vgic_release_lpi_locked() xarray node freed --> __xa_erase(.., intid) xa_unlock_irqrestore() xa_lock_irqsave() xa_load(.., intid) == NULL vgic_try_get_irq_ref(NULL) == false __xa_store(.., intid, irq, 0) <-- xarray node was freed, gfp=0 cannot allocate, returns -ENOMEM This can happen e.g. if the guest issues a DISCARD while the LPI is still referenced from a vCPU's active-pending list (ap_list), and the same INTID is re-mapped via MAPTI. Mitigate this by passing GFP_NOWAIT to __xa_store(), so that the allocation can happen under the lock in the rare case that this condition is hit. Add __GFP_ACCOUNT as well to match xa_reserve_irq()'s flags. Reported-by: Sashiko Fixes: 1d6f83f60f79 ("KVM: arm64: vgic: Store LPIs in an xarray") Signed-off-by: Carlos López --- arch/arm64/kvm/vgic/vgic-its.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c index 468533245727..eda5692c178f 100644 --- a/arch/arm64/kvm/vgic/vgic-its.c +++ b/arch/arm64/kvm/vgic/vgic-its.c @@ -124,7 +124,8 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid, * holds before freeing it, as otherwise someone else could still * hold a pointer to the evicted struct. */ - oldirq = __xa_store(&dist->lpi_xa, intid, irq, 0); + oldirq = __xa_store(&dist->lpi_xa, intid, irq, + GFP_NOWAIT | __GFP_ACCOUNT); ret = xa_err(oldirq); if (!ret && oldirq && !WARN_ON_ONCE(refcount_read(&oldirq->refcount) || -- 2.51.0