iommu/vt-d: Avoid memory allocation in iommu_suspend()

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

iommu/vt-d: Avoid memory allocation in iommu_suspend()

The iommu_suspend() syscore suspend callback is invoked with IRQ disabled.

Allocating memory with the GFP_KERNEL flag may re-enable IRQs during

the suspend callback, which can cause intermittent suspend/hibernation

problems with the following kernel traces:

Calling iommu_suspend+0x0/0x1d0

------------[ cut here ]------------

WARNING: CPU: 0 PID: 15 at kernel/time/timekeeping.c:868 ktime_get+0x9b/0xb0

...

CPU: 0 PID: 15 Comm: rcu_preempt Tainted: G U E 6.3-intel #r1

RIP: 0010:ktime_get+0x9b/0xb0

...

Call Trace:

<IRQ>

tick_sched_timer+0x22/0x90

? __pfx_tick_sched_timer+0x10/0x10

__hrtimer_run_queues+0x111/0x2b0

hrtimer_interrupt+0xfa/0x230

__sysvec_apic_timer_interrupt+0x63/0x140

sysvec_apic_timer_interrupt+0x7b/0xa0

</IRQ>

<TASK>

asm_sysvec_apic_timer_interrupt+0x1f/0x30

...

------------[ cut here ]------------

Interrupts enabled after iommu_suspend+0x0/0x1d0

WARNING: CPU: 0 PID: 27420 at drivers/base/syscore.c:68 syscore_suspend+0x147/0x270

CPU: 0 PID: 27420 Comm: rtcwake Tainted: G U W E 6.3-intel #r1

RIP: 0010:syscore_suspend+0x147/0x270

...

Call Trace:

<TASK>

hibernation_snapshot+0x25b/0x670

hibernate+0xcd/0x390

state_store+0xcf/0xe0

kobj_attr_store+0x13/0x30

sysfs_kf_write+0x3f/0x50

kernfs_fop_write_iter+0x128/0x200

vfs_write+0x1fd/0x3c0

ksys_write+0x6f/0xf0

__x64_sys_write+0x1d/0x30

do_syscall_64+0x3b/0x90

entry_SYSCALL_64_after_hwframe+0x72/0xdc

Given that only 4 words memory is needed, avoid the memory allocation in

iommu_suspend().