testing/cxl: Fix abused pci_bus_read_config_word() on platform device

The cxl_region_shared_upstream_bandwidth_update() in clx_core works on
PCI/PCIe CXL device only while cxl_test was implemeneted by platform
device.

Mock a cxl_region_shared_upstream_bandwidth_update() which does nothing
for cxl_core so that the cxl_test goes well.

Abuse cxl_region_shared_upstream_bandwidth_update() on platform device
will cause a kernel panic with calltrace:
 platform cxl_host_bridge.3: host supports CXL (restricted)
 Oops: general protection fault, probably for non-canonical address 0x3ef17856fcae4fbd: 0000 [#1] PREEMPT SMP PTI
 CPU: 1 UID: 0 PID: 9167 Comm: cxl Kdump: loaded Tainted: G           OE      6.12.0-rc3-master+ torvalds#66
 Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE
 Hardware name: LENOVO 90CXCTO1WW/, BIOS FCKT70AUS 04/23/2015
 RIP: 0010:pci_bus_read_config_word+0x1c/0x60
 Code: 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 44 00 00 53 b8 87 00 00 00 48 83 ec 08 c7 44 24 04 00 00 00 00 f6 c2 01 75 29 <48> 8b 87 c0 00 00 00 48 89 cb 4c 8d 44 24 04 b9 02 00 00 00 48 8b
 RSP: 0018:ffffa115034dfbb8 EFLAGS: 00010246
 RAX: 0000000000000087 RBX: 0000000000000012 RCX: ffffa115034dfbfe
 RDX: 0000000000000016 RSI: 000000006f4e2f4e RDI: 3ef17856fcae4efd
 RBP: ffff8cc229121b48 R08: 0000000000000010 R09: 0000000000000000
 R10: 0000000000000001 R11: ffff8cc225434360 R12: ffffa115034dfbfe
 R13: 0000000000000000 R14: ffff8cc2f119a080 R15: ffffa115034dfc50
 FS:  00007f31d93537c0(0000) GS:ffff8cc510a80000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 00007f31d95f3370 CR3: 00000001163ea001 CR4: 00000000001726f0
 Call Trace:
  <TASK>
  ? __die_body.cold+0x19/0x27
  ? die_addr+0x38/0x60
  ? exc_general_protection+0x1f5/0x4b0
  ? asm_exc_general_protection+0x22/0x30
  ? pci_bus_read_config_word+0x1c/0x60
  pcie_capability_read_word+0x93/0xb0
  pcie_link_speed_mbps+0x18/0x50
  cxl_pci_get_bandwidth+0x18/0x60 [cxl_core]
  cxl_endpoint_gather_bandwidth.constprop.0+0xf4/0x230 [cxl_core]
  ? xas_store+0x54/0x660
  ? preempt_count_add+0x69/0xa0
  ? _raw_spin_lock+0x13/0x40
  ? __kmalloc_cache_noprof+0xe7/0x270
  cxl_region_shared_upstream_bandwidth_update+0x9c/0x790 [cxl_core]
  cxl_region_attach+0x520/0x7e0 [cxl_core]
  store_targetN+0xf2/0x120 [cxl_core]
  kernfs_fop_write_iter+0x13a/0x1f0
  vfs_write+0x23b/0x410
  ksys_write+0x53/0xd0
  do_syscall_64+0x62/0x180
  entry_SYSCALL_64_after_hwframe+0x76/0x7e

And Ying also reported a KASAN error with similar calltrace.

Reported-by: "Huang, Ying" <[email protected]>
Closes: https://lore.kernel.org/linux-cxl/[email protected]/
Fixes: a5ab0de ("cxl: Calculate region bandwidth of targets with shared upstream link")
Signed-off-by: Li Zhijian <[email protected]>

tools/testing/cxl/Kbuild

@@ -15,6 +15,7 @@ ldflags-y += --wrap=devm_cxl_add_rch_dport
 ldflags-y += --wrap=cxl_rcd_component_reg_phys
 ldflags-y += --wrap=cxl_endpoint_parse_cdat
 ldflags-y += --wrap=cxl_dport_init_ras_reporting
+ldflags-y += --wrap=cxl_region_shared_upstream_bandwidth_update
 
 DRIVERS := ../../../drivers
 CXL_SRC := $(DRIVERS)/cxl
@@ -61,6 +62,7 @@ cxl_core-y += $(CXL_CORE_SRC)/pci.o
 cxl_core-y += $(CXL_CORE_SRC)/hdm.o
 cxl_core-y += $(CXL_CORE_SRC)/pmu.o
 cxl_core-y += $(CXL_CORE_SRC)/cdat.o
+cxl_core-y += mock_cdat.o
 cxl_core-$(CONFIG_TRACING) += $(CXL_CORE_SRC)/trace.o
 cxl_core-$(CONFIG_CXL_REGION) += $(CXL_CORE_SRC)/region.o
 cxl_core-y += config_check.o

tools/testing/cxl/mock_cdat.c

@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* Copyright (c) 2024 FUJITSU LIMITED. All rights reserved. */
+
+#include <cxl.h>
+
+void __wrap_cxl_region_shared_upstream_bandwidth_update(struct cxl_region *cxlr)
+{
+}