Re: [PATCH v3 1/5] drm/xe/bo: fix alignment with non-4KiB kernel page sizes

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Wed, Jul 23, 2025 at 04:45:13PM +0900, Simon Richter wrote:
> From: Mingcong Bai <jeffbai@aosc.io>
> 
> The bo/ttm interfaces with kernel memory mapping from dedicated GPU
> memory. It is not correct to assume that SZ_4K would suffice for page
> alignment as there are a few hardware platforms that commonly uses non-
> 4KiB pages - for instance, 16KiB is the most commonly used kernel page
> size used on Loongson devices (of the LoongArch architecture).
> 
> Per our testing, Intel Xe/Alchemist/Battlemage families of GPUs works on
> Loongson platforms so long as "Above 4G Decoding" was enabled and
> "Resizable BAR" was set to auto in the UEFI firmware settings.
> 
> Without this fix, the kernel will hang at a kernel BUG():
> 
> [    7.425445] ------------[ cut here ]------------
> [    7.430032] kernel BUG at drivers/gpu/drm/drm_gem.c:181!
> [    7.435330] Oops - BUG[#1]:
> [    7.438099] CPU: 0 UID: 0 PID: 102 Comm: kworker/0:4 Tainted: G            E      6.13.3-aosc-main-00336-g60829239b300-dirty #3
> [    7.449511] Tainted: [E]=UNSIGNED_MODULE
> [    7.453402] Hardware name: Loongson Loongson-3A6000-HV-7A2000-1w-V0.1-EVB/Loongson-3A6000-HV-7A2000-1w-EVB-V1.21, BIOS Loongson-UDK2018-V4.0.05756-prestab
> [    7.467144] Workqueue: events work_for_cpu_fn
> [    7.471472] pc 9000000001045fa4 ra ffff8000025331dc tp 90000001010c8000 sp 90000001010cb960
> [    7.479770] a0 900000012a3e8000 a1 900000010028c000 a2 000000000005d000 a3 0000000000000000
> [    7.488069] a4 0000000000000000 a5 0000000000000000 a6 0000000000000000 a7 0000000000000001
> [    7.496367] t0 0000000000001000 t1 9000000001045000 t2 0000000000000000 t3 0000000000000000
> [    7.504665] t4 0000000000000000 t5 0000000000000000 t6 0000000000000000 t7 0000000000000000
> [    7.504667] t8 0000000000000000 u0 90000000029ea7d8 s9 900000012a3e9360 s0 900000010028c000
> [    7.504668] s1 ffff800002744000 s2 0000000000000000 s3 0000000000000000 s4 0000000000000001
> [    7.504669] s5 900000012a3e8000 s6 0000000000000001 s7 0000000000022022 s8 0000000000000000
> [    7.537855]    ra: ffff8000025331dc ___xe_bo_create_locked+0x158/0x3b0 [xe]
> [    7.544893]   ERA: 9000000001045fa4 drm_gem_private_object_init+0xcc/0xd0
> [    7.551639]  CRMD: 000000b0 (PLV0 -IE -DA +PG DACF=CC DACM=CC -WE)
> [    7.557785]  PRMD: 00000004 (PPLV0 +PIE -PWE)
> [    7.562111]  EUEN: 00000000 (-FPE -SXE -ASXE -BTE)
> [    7.566870]  ECFG: 00071c1d (LIE=0,2-4,10-12 VS=7)
> [    7.571628] ESTAT: 000c0000 [BRK] (IS= ECode=12 EsubCode=0)
> [    7.577163]  PRID: 0014d000 (Loongson-64bit, Loongson-3A6000-HV)
> [    7.583128] Modules linked in: xe(E+) drm_gpuvm(E) drm_exec(E) drm_buddy(E) gpu_sched(E) drm_suballoc_helper(E) drm_display_helper(E) loongson(E) r8169(E) cec(E) rc_core(E) realtek(E) i2c_algo_bit(E) tpm_tis_spi(E) led_class(E) hid_generic(E) drm_ttm_helper(E) ttm(E) drm_client_lib(E) drm_kms_helper(E) sunrpc(E) la_ow_syscall(E) i2c_dev(E)
> [    7.613049] Process kworker/0:4 (pid: 102, threadinfo=00000000bc26ebd1, task=0000000055480707)
> [    7.621606] Stack : 0000000000000000 3030303a6963702b 000000000005d000 0000000000000000
> [    7.629563]         0000000000000001 0000000000000000 0000000000000000 8e1bfae42b2f7877
> [    7.637519]         000000000005d000 900000012a3e8000 900000012a3e9360 0000000000000000
> [    7.645475]         ffffffffffffffff 0000000000000000 0000000000022022 0000000000000000
> [    7.653431]         0000000000000001 ffff800002533660 0000000000022022 9000000000234470
> [    7.661386]         90000001010cba28 0000000000001000 0000000000000000 000000000005c300
> [    7.669342]         900000012a3e8000 0000000000000000 0000000000000001 900000012a3e8000
> [    7.677298]         ffffffffffffffff 0000000000022022 900000012a3e9498 ffff800002533a14
> [    7.685254]         0000000000022022 0000000000000000 900000000209c000 90000000010589e0
> [    7.693209]         90000001010cbab8 ffff8000027c78c0 fffffffffffff000 900000012a3e8000
> [    7.701165]         ...
> [    7.703588] Call Trace:
> [    7.703590] [<9000000001045fa4>] drm_gem_private_object_init+0xcc/0xd0
> [    7.712496] [<ffff8000025331d8>] ___xe_bo_create_locked+0x154/0x3b0 [xe]
> [    7.719268] [<ffff80000253365c>] __xe_bo_create_locked+0x228/0x304 [xe]
> [    7.725951] [<ffff800002533a10>] xe_bo_create_pin_map_at_aligned+0x70/0x1b0 [xe]
> [    7.733410] [<ffff800002533c7c>] xe_managed_bo_create_pin_map+0x34/0xcc [xe]
> [    7.740522] [<ffff800002533d58>] xe_managed_bo_create_from_data+0x44/0xb0 [xe]
> [    7.747807] [<ffff80000258d19c>] xe_uc_fw_init+0x3ec/0x904 [xe]
> [    7.753814] [<ffff80000254a478>] xe_guc_init+0x30/0x3dc [xe]
> [    7.759553] [<ffff80000258bc04>] xe_uc_init+0x20/0xf0 [xe]
> [    7.765121] [<ffff800002542abc>] xe_gt_init_hwconfig+0x5c/0xd0 [xe]
> [    7.771461] [<ffff800002537204>] xe_device_probe+0x240/0x588 [xe]
> [    7.777627] [<ffff800002575448>] xe_pci_probe+0x6c0/0xa6c [xe]
> [    7.783540] [<9000000000e9828c>] local_pci_probe+0x4c/0xb4
> [    7.788989] [<90000000002aa578>] work_for_cpu_fn+0x20/0x40
> [    7.794436] [<90000000002aeb50>] process_one_work+0x1a4/0x458
> [    7.800143] [<90000000002af5a0>] worker_thread+0x304/0x3fc
> [    7.805591] [<90000000002bacac>] kthread+0x114/0x138
> [    7.810520] [<9000000000241f64>] ret_from_kernel_thread+0x8/0xa4
> [    7.816489]
> [    7.817961] Code: 4c000020  29c3e2f9  53ff93ff <002a0001> 0015002c  03400000  02ff8063  29c04077  001500f7
> [    7.827651]
> [    7.829140] ---[ end trace 0000000000000000 ]---
> 
> Revise all instances of `SZ_4K' with `PAGE_SIZE' and revise the call to
> `drm_gem_private_object_init()' in `*___xe_bo_create_locked()' (last call
> before BUG()) to use `size_t aligned_size' calculated from `PAGE_SIZE' to
> fix the above error.
> 
> Cc: <stable@vger.kernel.org>
> Fixes: 4e03b584143e ("drm/xe/uapi: Reject bo creation of unaligned size")
> Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
> Tested-by: Mingcong Bai <jeffbai@aosc.io>
> Tested-by: Wenbin Fang <fangwenbin@vip.qq.com>
> Tested-by: Haien Liang <27873200@qq.com>
> Tested-by: Jianfeng Liu <liujianfeng1994@gmail.com>
> Tested-by: Shirong Liu <lsr1024@qq.com>
> Tested-by: Haofeng Wu <s2600cw2@126.com>
> Link: https://github.com/FanFansfan/loongson-linux/commit/22c55ab3931c32410a077b3ddb6dca3f28223360
> Link: https://t.me/c/1109254909/768552
> Co-developed-by: Shang Yatsen <429839446@qq.com>
> Signed-off-by: Shang Yatsen <429839446@qq.com>
> Signed-off-by: Mingcong Bai <jeffbai@aosc.io>

please remember to sign-off whenever you are sending or handling other's patches

> ---
>  drivers/gpu/drm/xe/xe_bo.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xe/xe_bo.c b/drivers/gpu/drm/xe/xe_bo.c
> index 00ce067d5fd3..649e6d0e05a1 100644
> --- a/drivers/gpu/drm/xe/xe_bo.c
> +++ b/drivers/gpu/drm/xe/xe_bo.c
> @@ -1861,9 +1861,9 @@ struct xe_bo *___xe_bo_create_locked(struct xe_device *xe, struct xe_bo *bo,
>  		flags |= XE_BO_FLAG_INTERNAL_64K;
>  		alignment = align >> PAGE_SHIFT;
>  	} else {
> -		aligned_size = ALIGN(size, SZ_4K);
> +		aligned_size = ALIGN(size, PAGE_SIZE);
>  		flags &= ~XE_BO_FLAG_INTERNAL_64K;
> -		alignment = SZ_4K >> PAGE_SHIFT;
> +		alignment = PAGE_SIZE >> PAGE_SHIFT;

okay, this is definitely right

>  	}
>  
>  	if (type == ttm_bo_type_device && aligned_size != size)
> @@ -1887,7 +1887,7 @@ struct xe_bo *___xe_bo_create_locked(struct xe_device *xe, struct xe_bo *bo,
>  #endif
>  	INIT_LIST_HEAD(&bo->vram_userfault_link);
>  
> -	drm_gem_private_object_init(&xe->drm, &bo->ttm.base, size);
> +	drm_gem_private_object_init(&xe->drm, &bo->ttm.base, aligned_size);

but this is strange.
think that we could get rid of the aligned_size variable and only go with
size = ALIGN(size, PAGE_SIZE)

but then there are some checks in between on the alignment
and different handling in different if conditions.

We need further clean-up there to make the change obviously right first.

>  
>  	if (resv) {
>  		ctx.allow_res_evict = !(flags & XE_BO_FLAG_NO_RESV_EVICT);
> -- 
> 2.47.2
>