Warding Flare

[Pex]

When the Light Cleric uses Warding Flare is the disadvantage imposed just for one attack or all attacks an opponent makes against the cleric that round? The DM was fine ruling it affected all attacks, but I would like to know how it's supposed to be. It's not clear.

[Biggstick]

Also at 1st level, you can interpose divine light between yourself and an attacking enemy. When you are attacked by a creature within 30 feet of you that you can see, you can use your reaction to impose disadvantage on the attack roll, causing light to flare before the attacker before it hits or misses. An attacker that can’t be blinded is immune to this feature.


The bolded part is what's relevant here. You can only impose disadvantage on one attack roll.