qemu/hw/device-assignment: questions about msix_table_page

Sheng, Marcelo,
I've been reading code in qemu/hw/device-assignment.c, and
I have a couple of questions about msi-x implementation:
1. What is the reason that msix_table_page is allocated
with mmap and not with e.g. malloc?
2. msix_table_page has the guest view of the msix table for the device. However, even this memory isn't mapped into guest directly, instead msix_mmio_read/msix_mmio_write perform the write in qemu. Won't it be possible to map this page directly into
guest memory, reducing the overhead for table writes?

Could you shed light on this for me please?
Thanks,

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MST