What could stop the Nvidia frenzy?

IF today’s stockmarkets have their version of the great wildebeest migration, it is the stampede of the Nvidia bulls. Wall Street is no Serengeti, and Jim Cramer’s high-pitched narration no match for the dulcet tones of Sir David Attenborough. But in other respects investors’ headlong rush into the American chipmaker’s shares has been every bit as enthralling a spectacle.