KVM: selftests: Verify KVM preserves userspace writes to "durable" MSRs

KVM: selftests: Verify KVM preserves userspace writes to "durable" MSRs

Assert that KVM provides "read what you wrote" semantics for all "durable"
MSRs (for lack of a better name).  The extra coverage is cheap from a
runtime performance perspective, and verifying the behavior in the common
helper avoids gratuitous copy+paste in individual tests.

Note, this affects all tests that set MSRs from userspace!

Link: https://lore.kernel.org/r/20230311004618.920745-13-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>