Running the following command on Juno triggers the warning:

 $ perf record -e cs_etm// -m ,128M ...

 ------------[ cut here ]------------
 WARNING: CPU: 1 PID: 412 at mm/page_alloc.c:4453 __alloc_pages+0x334/0x1420
 CPU: 1 PID: 412 Comm: perf Not tainted 6.5.0-rc3+ #181
 Hardware name: ARM LTD ARM Juno Development Platform/ARM Juno Development Platform, BIOS EDK II Feb  1 2019
 pstate: 20000005 (nzCv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
 pc : __alloc_pages+0x334/0x1420
 lr : dma_common_alloc_pages+0x108/0x138
 sp : ffffffc087fb7440
 x29: ffffffc087fb7440 x28: 0000000000000000 x27: ffffffc07e48fba0
 x26: 0000000000000001 x25: 000000000000000f x24: ffffffc081f24880
 x23: 0000000000000cc0 x22: ffffff88012b6f08 x21: 0000000008000000
 x20: ffffff8801433000 x19: 0000000000000000 x18: 0000000000000000
 x17: ffffffc080316e5c x16: ffffffc07e46406c x15: ffffffc0803af580
 x14: ffffffc08036b460 x13: ffffffc080025cbc x12: ffffffb8108c3fc4
 x11: 1ffffff8108c3fc3 x10: 1ffffff810ff6eac x9 : 00000000f204f204
 x8 : 000000000000f204 x7 : 00000000f2f2f2f2 x6 : 00000000f3f3f3f3
 x5 : 0000000000000001 x4 : 0000000000000000 x3 : 0000000000000000
 x2 : 0000000000000cc0 x1 : 0000000000000000 x0 : ffffffc085333000
 Call trace:
  __alloc_pages+0x334/0x1420
  dma_common_alloc_pages+0x108/0x138
  __dma_alloc_pages+0xf4/0x108
  dma_alloc_pages+0x18/0x30
  tmc_etr_alloc_flat_buf+0xa0/0x190 [coresight_tmc]
  tmc_alloc_etr_buf.constprop.0+0x124/0x298 [coresight_tmc]
  alloc_etr_buf.constprop.0.isra.0+0x88/0xc8 [coresight_tmc]
  tmc_alloc_etr_buffer+0x164/0x2f0 [coresight_tmc]
  etm_setup_aux+0x32c/0x520 [coresight]
  rb_alloc_aux+0x29c/0x3f8
  perf_mmap+0x59c/0xce0
  mmap_region+0x340/0x10e0
  do_mmap+0x48c/0x580
  vm_mmap_pgoff+0x160/0x248
  ksys_mmap_pgoff+0x1e8/0x278
  __arm64_sys_mmap+0x8c/0xb8

With the flat mode, we only attempt to allocate large memory if there is an IOMMU
connected to the ETR. If the allocation fails, we always have a fallback path
and return an error if nothing else worked. So, suppress the warning for flat
mode allocations.

Cc: Mike Leach <mike.leach@linaro.org>
Cc: James Clark <james.clark@arm.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: James Clark <james.clark@arm.com>
Link: https://lore.kernel.org/r/20230817161951.658534-1-suzuki.poulose@arm.com