[PATCH] cxl: read MEMDEV_STATUS register iff the device has it

[Zhi Wang <zhiw@nvidia.com>]

Before accessing the CXL device memory after reset/power-on, the driver
needs to ensure the device memory media is ready.

However, not every CXL device implements the CXL memory device register
groups. E.g. a CXL type-2 device. Thus calling cxl_await_media_ready()
on these devcie will lead to a kernel panic. This problem was found when
testing the emulated CXL type-2 device without a CXL memory device
register.

[   97.662720] BUG: kernel NULL pointer dereference, address: 0000000000000000
[   97.663963] #PF: supervisor read access in kernel mode
[   97.664860] #PF: error_code(0x0000) - not-present page
[   97.665753] PGD 0 P4D 0
[   97.666198] Oops: Oops: 0000 [#1] PREEMPT SMP NOPTI
[   97.667053] CPU: 8 UID: 0 PID: 7340 Comm: qemu-system-x86 Tainted: G            E      6.11.0-rc2+ #52
[   97.668656] Tainted: [E]=UNSIGNED_MODULE
[   97.669340] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
[   97.671243] RIP: 0010:cxl_await_media_ready+0x1ac/0x1d0
[   97.672157] Code: e9 03 ff ff ff 0f b7 1d d6 80 31 01 48 8b 7d b8 89 da 48 c7 c6 60 52 c6 b0 e8 00 46 f6 ff e9 27 ff ff ff 49 8b 86 a0 00 00 00 <48> 8b 00 83 e0 0c 48 83 f8 04 0f 94 c0 0f b6 c0 8d 44 80 fb e9 0c
[   97.675391] RSP: 0018:ffffb5bac7627c20 EFLAGS: 00010246
[   97.676298] RAX: 0000000000000000 RBX: 000000000000003c RCX: 0000000000000000
[   97.677527] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
[   97.678733] RBP: ffffb5bac7627c70 R08: 0000000000000000 R09: 0000000000000000
[   97.679951] R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
[   97.681144] R13: ffff9ef9028a8000 R14: ffff9ef90c1d1a28 R15: 0000000000000000
[   97.682370] FS:  00007386aa4f3d40(0000) GS:ffff9efa77200000(0000) knlGS:0000000000000000
[   97.683721] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   97.684703] CR2: 0000000000000000 CR3: 0000000169a14003 CR4: 0000000000770ef0
[   97.685909] PKRU: 55555554
[   97.686397] Call Trace:
[   97.686819]  <TASK>
[   97.687243]  ? show_regs+0x6c/0x80
[   97.687840]  ? __die+0x24/0x80
[   97.688391]  ? page_fault_oops+0x155/0x570
[   97.689090]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.689973]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.690848]  ? __vunmap_range_noflush+0x420/0x4e0
[   97.691700]  ? do_user_addr_fault+0x4b2/0x870
[   97.692606]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.693502]  ? exc_page_fault+0x82/0x1b0
[   97.694200]  ? asm_exc_page_fault+0x27/0x30
[   97.694975]  ? cxl_await_media_ready+0x1ac/0x1d0
[   97.695816]  vfio_cxl_core_enable+0x386/0x800 [vfio_cxl_core]
[   97.696829]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.697685]  cxl_open_device+0xa6/0xd0 [cxl_accel_vfio_pci]
[   97.698673]  vfio_df_open+0xcb/0xf0
[   97.699313]  vfio_group_fops_unl_ioctl+0x294/0x720
[   97.700149]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.701011]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.701858]  __x64_sys_ioctl+0xa3/0xf0
[   97.702536]  x64_sys_call+0x11ad/0x25f0
[   97.703214]  do_syscall_64+0x7e/0x170
[   97.703878]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.704726]  ? do_syscall_64+0x8a/0x170
[   97.705425]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.706282]  ? kvm_device_ioctl+0xae/0x130 [kvm]
[   97.707135]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.708001]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.708853]  ? syscall_exit_to_user_mode+0x4e/0x250
[   97.709724]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.710609]  ? do_syscall_64+0x8a/0x170
[   97.711300]  ? srso_alias_return_thunk+0x5/0xfbef5
[   97.712132]  ? exc_page_fault+0x93/0x1b0
[   97.712839]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[   97.713735] RIP: 0033:0x7386ab124ded
[   97.714382] Code: 04 25 28 00 00 00 48 89 45 c8 31 c0 48 8d 45 10 c7 45 b0 10 00 00 00 48 89 45 b8 48 8d 45 d0 48 89 45 c0 b8 10 00 00 00 0f 05 <89> c2 3d 00 f0 ff ff 77 1a 48 8b 45 c8 64 48 2b 04 25 28 00 00 00
[   97.717664] RSP: 002b:00007ffcda2a6480 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
[   97.718965] RAX: ffffffffffffffda RBX: 00006293226d9f20 RCX: 00007386ab124ded
[   97.720222] RDX: 00006293226db730 RSI: 0000000000003b6a RDI: 0000000000000009
[   97.721522] RBP: 00007ffcda2a64d0 R08: 00006293214e9010 R09: 0000000000000007
[   97.722858] R10: 00006293226db730 R11: 0000000000000246 R12: 00006293226e0880
[   97.724193] R13: 00006293226db730 R14: 00007ffcda2a7740 R15: 00006293226d94f0
[   97.725491]  </TASK>
[   97.725883] Modules linked in: cxl_accel_vfio_pci(E) vfio_cxl_core(E) vfio_pci_core(E) snd_seq_dummy(E) snd_hrtimer(E) snd_seq(E) snd_seq_device(E) snd_timer(E) snd(E) soundcore(E) qrtr(E) intel_rapl_msr(E) intel_rapl_common(E) kvm_amd(E) ccp(E) binfmt_misc(E) kvm(E) crct10dif_pclmul(E) crc32_pclmul(E) polyval_clmulni(E) polyval_generic(E) ghash_clmulni_intel(E) sha256_ssse3(E) sha1_ssse3(E) aesni_intel(E) i2c_i801(E) crypto_simd(E) cryptd(E) i2c_smbus(E) lpc_ich(E) joydev(E) input_leds(E) mac_hid(E) serio_raw(E) msr(E) parport_pc(E) ppdev(E) lp(E) parport(E) efi_pstore(E) dmi_sysfs(E) qemu_fw_cfg(E) autofs4(E) bochs(E) e1000e(E) drm_vram_helper(E) psmouse(E) drm_ttm_helper(E) ahci(E) ttm(E) libahci(E)
[   97.736690] CR2: 0000000000000000
[   97.737285] ---[ end trace 0000000000000000 ]---

Only read MEMDEV_STATUS register for ensuring media ready when the device
has it.

Signed-off-by: Zhi Wang <zhiw@nvidia.com>
---
 drivers/cxl/core/pci.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/cxl/core/pci.c b/drivers/cxl/core/pci.c
index 51132a575b27..7a8ec4928da6 100644
--- a/drivers/cxl/core/pci.c
+++ b/drivers/cxl/core/pci.c
@@ -203,9 +203,11 @@ int cxl_await_media_ready(struct cxl_dev_state *cxlds)
 			return rc;
 	}
 
-	md_status = readq(cxlds->regs.memdev + CXLMDEV_STATUS_OFFSET);
-	if (!CXLMDEV_READY(md_status))
-		return -EIO;
+	if (cxlds->regs.memdev) {
+		md_status = readq(cxlds->regs.memdev + CXLMDEV_STATUS_OFFSET);
+		if (!CXLMDEV_READY(md_status))
+			return -EIO;
+	}
 
 	return 0;
 }
-- 
2.34.1