drm/amdgpu: fix NULL pointer dereference in amdgpu_gmc_filter_faults_remove

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

drm/amdgpu: fix NULL pointer dereference in amdgpu_gmc_filter_faults_remove

On APUs such as Raven and Renoir (GC 9.1.0, 9.2.2, 9.3.0), the ih1 and

ih2 interrupt ring buffers are not initialized. This is by design, as

these secondary IH rings are only available on discrete GPUs. See

vega10_ih_sw_init() which explicitly skips ih1/ih2 initialization when

AMD_IS_APU is set.

However, amdgpu_gmc_filter_faults_remove() unconditionally uses ih1 to

get the timestamp of the last interrupt entry. When retry faults are

enabled on APUs (noretry=0), this function is called from the SVM page

fault recovery path, resulting in a NULL pointer dereference when

amdgpu_ih_decode_iv_ts_helper() attempts to access ih->ring[].

The crash manifests as:

BUG: kernel NULL pointer dereference, address: 0000000000000004

RIP: 0010:amdgpu_ih_decode_iv_ts_helper+0x22/0x40 [amdgpu]

Call Trace:

amdgpu_gmc_filter_faults_remove+0x60/0x130 [amdgpu]

svm_range_restore_pages+0xae5/0x11c0 [amdgpu]

amdgpu_vm_handle_fault+0xc8/0x340 [amdgpu]

gmc_v9_0_process_interrupt+0x191/0x220 [amdgpu]

amdgpu_irq_dispatch+0xed/0x2c0 [amdgpu]

amdgpu_ih_process+0x84/0x100 [amdgpu]

This issue was exposed by commit 1446226d32a4 ("drm/amdgpu: Remove GC HW

IP 9.3.0 from noretry=1") which changed the default for Renoir APU from

noretry=1 to noretry=0, enabling retry fault handling and thus

exercising the buggy code path.

Fix this by adding a check for ih1.ring_size before attempting to use

it. Also restore the soft_ih support from commit dd299441654f ("drm/amdgpu:

Rework retry fault removal"). This is needed if the hardware doesn't

support secondary HW IH rings.

v2: additional updates (Alex)

(cherry picked from commit 6ce8d536c80aa1f059e82184f0d1994436b1d526)