iommu/vt-d: Fix qi_batch NULL pointer with nested parent domain

In the Linux kernel, the following vulnerability has been resolved:

iommu/vt-d: Fix qi_batch NULL pointer with nested parent domain

The qi_batch is allocated when assigning cache tag for a domain. While

for nested parent domain, it is missed. Hence, when trying to map pages

to the nested parent, NULL dereference occurred. Also, there is potential

memleak since there is no lock around domain->qi_batch allocation.

To solve it, add a helper for qi_batch allocation, and call it in both

the __cache_tag_assign_domain() and __cache_tag_assign_parent_domain().

BUG: kernel NULL pointer dereference, address: 0000000000000200

#PF: supervisor read access in kernel mode

#PF: error_code(0x0000) - not-present page

PGD 8104795067 P4D 0

Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI

CPU: 223 UID: 0 PID: 4357 Comm: qemu-system-x86 Not tainted 6.13.0-rc1-00028-g4b50c3c3b998-dirty #2632

Call Trace:

? __die+0x24/0x70

? page_fault_oops+0x80/0x150

? do_user_addr_fault+0x63/0x7b0

? exc_page_fault+0x7c/0x220

? asm_exc_page_fault+0x26/0x30

? cache_tag_flush_range_np+0x13c/0x260

intel_iommu_iotlb_sync_map+0x1a/0x30

iommu_map+0x61/0xf0

batch_to_domain+0x188/0x250

iopt_area_fill_domains+0x125/0x320

? rcu_is_watching+0x11/0x50

iopt_map_pages+0x63/0x100

iopt_map_common.isra.0+0xa7/0x190

iopt_map_user_pages+0x6a/0x80

iommufd_ioas_map+0xcd/0x1d0

iommufd_fops_ioctl+0x118/0x1c0

__x64_sys_ioctl+0x93/0xc0

do_syscall_64+0x71/0x140

entry_SYSCALL_64_after_hwframe+0x76/0x7e