While at a customer site, migrating an old vSphere 5.5 environment to 6.5, several hosts suddenly crashed with a PSOD during the migration. Long story short, we got hit by this: VMware KB 2147958: ESXi 6.5 host fails with PSOD: GP Exception 13 in multiple VMM world at VmAnon_AllocVmmPages (2147958)
It turned out that a bunch of the VMs we were vMotioning from the old environment had the cpuid.corePerSocket advanced setting set in the .vmx file, and this can cause ESXi 6.5 to enter a state of panic, and in our case it certainly did.
Upgrading the hosts to 6.5a, like the knowledgebase article states, alleviated the issue and we did not experience PSOD’s again while migrating the 100+ VMs from the old environment to the new one.