quoted

-	wrmsrl(MSR_CSTAR, (unsigned long)entry_SYSCALL_compat);
+	/*
+	 * CSTAR is not needed on Intel because it doesn't support
+	 * 32bit SYSCALL, but only SYSENTER. On a TDX guest
+	 * it leads to a #GP.

Sigh. Above you write it raises #VE, but now it's #GP !?!

The unhandled #VE trap is handled like a #GP, which is then caught by 
the kernel wrmsr code.

So both are correct.

         Intel CPUs do not support 32-bit SYSCALL. Writing to MSR_CSTAR
         is normaly ignored by the CPU, but raises a #VE trap in a TDX
         guest.

Hmm?