MOVDQU vs MOVDQA Instruction (x86/x64 assembly) better insights

Question

First of all, let's start with the following links about MOVDQA and MOVDQU which are already in this community:

• MOVDQU instruction + page boundary
• MOVUPD vs. MOVDQU (x86/x64 assembly)
• Difference between MOVDQA and MOVAPS x86 instructions?
• Assembly "movdqa" access violation

Here, I am sharing links that describe these two instructions

• https://c9x.me/x86/html/file_module_x86_id_184.html
• https://mudongliang.github.io/x86/html/file_module_x86_id_183.html

Now let's dive into my problem. I am using Linux(64-bit). I have created a test project in C++ that uses several assembly implementations. I need better insight using MOVDQA and MOVDQU that loads data to xmm registers. Here I am sharing some of my experiments:

---

    // Initialization 1
    std::string_view lhs{"Once upon a time in Germany"}; // length = 27
    std::string_view rhs = lhs.substr(20, 7);            // RHS points to "germany"

    # Experiment 1.1
    # Here: %rax = lhs, %rsi = rhs
    movdqa (%rax), %xmm11           // SIGSEGV in this line, although it has enough memory allocations
    movdqa (%rsi), %xmm12

    # Experiment 1.2
    # Here: %rax = lhs, %rsi = rhs
    movdqu (%rax), %xmm11           // data successfully loaded into register
    movdqu (%rsi), %xmm12           // data successfully loaded into register with some garbage

---

    // Initialization 2
    void *lhs = mmap ( NULL, 27*sizeof(unsigned char), PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, 0, 0 );
    void *rhs = lhs + 20;

    # Experiment 2.1
    # Here: %rax = lhs, %rsi = rhs
    movdqa (%rax), %xmm11           // data successfully loaded into register
    movdqa (%rsi), %xmm12           // SIGSEGV in this line... Expected!

    # Experiment 2.2
    # Here: %rax = lhs, %rsi = rhs
    movdqu (%rax), %xmm11           // data successfully loaded into register
    movdqu (%rsi), %xmm12           // data successfully loaded into register with some garbage

---

    // Initialization 3
    unsigned char *lhs = new unsigned char[27];
    unsigned char *rhs = lhs + 20;

    # Experiment 3.1
    # Here: %rax = lhs, %rsi = rhs
    movdqa (%rax), %xmm11           // data successfully loaded into register
    movdqa (%rsi), %xmm12           // SIGSEGV in this line

    # Experiment 3.2
    # Here: %rax = lhs, %rsi = rhs
    movdqu (%rax), %xmm11           // data successfully loaded into register
    movdqu (%rsi), %xmm12           // data successfully loaded into register with some garbage

Questions:

• Can anyone explain experiment 1.1?
• It seems to me, using MOVDQU is always safe. If it's not, What are the scenarios MOVDQU throws SIGSSEGV?
• Also, What are the scenarios MOVDQA throws SIGSSEGV?
• Can anyone share any reference about showing the Performance using MOVDQA and MOVDQU (i.e which is faster)?