Air carrier Captain reported while flying near the Azerbaijan border the aircraft experienced GPS jamming. The Captain was concerned if the system would return to normal. The crew contacted maintenance for assistance.

Narrative

I was the RC (Relief Captain) and went on the first break shortly after takeoff from Delhi. After returning from my break we were near Azerbaijan and the FMS was using DME-DME to navigate. ANP (Actual NAV Performance) was good; less then .5.The GPS was not usable and did not display a position (early in the flight). Later; in Eastern Europe GPS began to show a Lat/Long but its differential displayed on POS REF Page 2 was 16.0; therefore unusable. The FMS was continuing to use DME-DME to navigate. We were all very concerned if the aircraft could continue to receive land based NAV aids once we flew toward Iceland; Greenland and northern Canada. I again went on my rest break.I returned from break approaching 50 degrees West on the North Atlantic track. The aircraft FMS was now using GPS as it navigation source. The Captain and FO (First Officer) had contacted maintenance and performed a maintenance procedure with them cycling circuit breakers to reset the GPS.Cause: GPS jamming or unreliability in the Middle and Far East. Suggestion. I am continually concerned whenever I have flights that fly near India; Pakistan; Israel; Syria; Turkey and Ukraine due to GPS jamming and general GPS position stability. Active management of RAD NAV Inhibits are required but sometimes the GPS never recovers for the FMC to use it for navigation. On this last flight when the Captain called maintenance they remotely checked our aircraft and found the hardware had hard GPS faults. Apparently this can not be fixed by pushing buttons on the CDU (Control Display Panel). Then what can the crew do? You are facing an Oceanic crossing without NAV Aids that provide accurate position information. That would force a divert to London or Iceland or descent below RVSM airspace (and therefore insufficient fuel to reach destination). I do not want to fly flights that put me in this position; I will avoid these flights in the future. Crews should be given the permission to call maintenance in this situation and if inflight analysis shows hard faults in GPS components then maintenance should authorize cycling specific circuit breakers to recover navigation capability.