accel/mshv: Handle overlapping mem mappings

QEMU maps certain regions into the guest multiple times, as seen in the
trace below. Currently the MSHV kernel driver will reject those
mappings. To workaround this, a record is kept (a static global list of
"slots", inspired by what the HVF accelerator has implemented). An
overlapping region is not registered at the hypervisor, and marked as
mapped=false. If there is an UNMAPPED_GPA exit, we can look for a slot
that is unmapped and would cover the GPA. In this case we map out the
conflicting slot and map in the requested region.

mshv_set_phys_mem       add=1 name=pc.bios
mshv_map_memory      => u_a=7ffff4e00000 gpa=00fffc0000 size=00040000
mshv_set_phys_mem       add=1 name=ioapic
mshv_set_phys_mem       add=1 name=hpet
mshv_set_phys_mem       add=0 name=pc.ram
mshv_unmap_memory       u_a=7fff67e00000 gpa=0000000000 size=80000000
mshv_set_phys_mem       add=1 name=pc.ram
mshv_map_memory         u_a=7fff67e00000 gpa=0000000000 size=000c0000
mshv_set_phys_mem       add=1 name=pc.rom
mshv_map_memory         u_a=7ffff4c00000 gpa=00000c0000 size=00020000
mshv_set_phys_mem       add=1 name=pc.bios
mshv_remap_attempt   => u_a=7ffff4e20000 gpa=00000e0000 size=00020000

The mapping table is guarded by a mutex for concurrent modification and
RCU mechanisms for concurrent reads. Writes occur rarely, but we'll have
to verify whether an unmapped region exist for each UNMAPPED_GPA exit,
which happens frequently.

Signed-off-by: Magnus Kulke <magnuskulke@linux.microsoft.com>
Link: https://lore.kernel.org/r/20250916164847.77883-24-magnuskulke@linux.microsoft.com
[Fix format strings for trace-events; mshv.h/mshv_int.h split. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

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