A vampire's bite deals 10 necrotic damage1 and also reduces the target's maximum hit points by the same amount. Suppose I am at full health with 50 hit points, and a vampire bites me twice. My maximum hit points are now reduced to 30. (My current hit points are even lower since the bite also deals piercing damage, but that's irrelevant to this question.) After the battle, my party cleric tries to heal this maximum hit point reduction by casting Greater Restoration on me, which can end
one effect reducing the target's hit point maximum
What is my maximum hit point value now, after having Greater Restoration cast on me once? Does it remove the effect of a single bite, or all bites?
1It's actually 3d6, but I'm abstracting the dice rolls since they're not relevant to the question.