KVM: selftests: Rework svm_nested_invalid_vmcb12_gpa

KVM: selftests: Rework svm_nested_invalid_vmcb12_gpa

The test currently allegedly makes sure that VMRUN causes a #GP in
vmcb12 GPA is valid but unmappable. However, it calls run_guest() with
an the test vmcb12 GPA, and the #GP is produced from VMLOAD, not VMRUN.

Additionally, the underlying logic just changed to match architectural
behavior, and all of VMRUN/VMLOAD/VMSAVE fail emulation if vmcb12 cannot
be mapped. The CPU still injects a #GP if the vmcb12 GPA exceeds
maxphyaddr.

Rework the test such to use the KVM_ONE_VCPU_TEST[_SUITE] harness, and
test all of VMRUN/VMLOAD/VMSAVE with both an invalid GPA (-1ULL) causing
a #GP, and a valid but unmappable GPA causing emulation failure. Execute
the instructions directly from L1 instead of run_guest() to make sure
the #GP or emulation failure is produced by the right instruction.

Leave the #VMEXIT with unmappable GPA test case as-is, but wrap it with
a test harness as well.

Opportunisitically drop gp_triggered, as the test already checks that
a #GP was injected through a SYNC. Also, use the first unmapped GPA
instead of the maximum legal GPA, as some CPUs inject a #GP for the
maximum legal GPA (likely in a reserved area).

Signed-off-by: Yosry Ahmed <yosry@kernel.org>
Link: https://patch.msgid.link/20260316202732.3164936-9-yosry@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>