How to load a avx-512 zmm register from a ioremap() address?

My goal is to create a PCIe transaction with more than 64b payload. For that I need to read an ioremap() address.

For 128b and 256b I can use xmm and ymm registers respectively and that works as expected.

Now, I'd like to do the same for 512b zmm registers (memory-like storage?!)

A code under license I'm not allowed to show here, uses assembly code for 256b:

void __iomem *addr;
uint8_t datareg[32];
[...]
// Read memory address to ymm (to have 256b at once):
asm volatile("vmovdqa %0,%%ymm1" : : "m"(*(volatile uint8_t * __force) addr));
// Copy ymm data to stack data: (to be able to use that in a gcc handled code)
asm volatile("vmovdqa %%ymm1,%0" :"=m"(datareg): :"memory");

This is to be used in a kernel module compiled with EXTRA_CFLAGS += -mavx2 -mavx512f to support AVX-512.

1. Why does this example use ymm1 and not a different register ymm0-2-3-4..15?
2. How can I read an address to a 512b zmm register?
3. How can I be sure the register won't be overwritten between the two asm lines?

Simply replacing ymm by zmm, gcc shows Error: operand size mismatch forvmovdqa'`.

If that code isn't correct or the best practice, let solve that first since I just started to dig into that.