[PATCH 1/1] drm/prime: Use sg_dma_len() macro to get sg's length

[Vivek Gautam]

After mapping a sg list we should use sg_dma_address(), and
sg_dma_len() macros to access sg->address and sg->length. Fix
the same for sg->length in drm_prime_sg_to_page_addr_arrays().

Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
---

This came while debugging one dmabuf import issue that we are seeing
on sdm845 target.
The dmabuf which is prepared by video (venus in this case), is imported
by drm device.
The import call flow looks like follows:

drm_gem_prime_import()
 - drm_gem_prime_import_dev()
   - dma_buf_attach() & dma_buf_map_attachment()
     - From dma_buf_map_attachment()
       - vb2_dma_sg_dmabuf_ops_map()
         - dma_map_sg(): this updates the sg->nents.

>From debugging, the sg table mapping results in sg's 'nents' to be less that
the original nents. Now drm device prepares the page information based on
this sg table, and messes up with the mappings, and we start seeing random
crashes as below from drm's memory space.

Although this change isn't helping to fix the issue currently, but
this fix seems the right thing to do.

One thing to notice is that, if we restore the sg->nents to
sg->orig_nents in vb2_dma_sg_dmabuf_ops_map(), we don't see the below
corruptions.

Any pointers on this will be highly appreciated.
Thanks.

------
[  338.070558] Unable to handle kernel paging request at virtual address 0000400000000038
[  338.078751] Mem abort info:
[  338.081671]   ESR = 0x96000004
[  338.084860]   Exception class = DABT (current EL), IL = 32 bits
[  338.090972]   SET = 0, FnV = 0
[  338.094139]   EA = 0, S1PTW = 0
[  338.097393] Data abort info:
[  338.100375]   ISV = 0, ISS = 0x00000004
[  338.104362]   CM = 0, WnR = 0
[  338.107446] [0000400000000038] address between user and kernel address ranges
[  338.114801] Internal error: Oops: 96000004 [#1] PREEMPT SMP
[  338.120527] Modules linked in: rfcomm uinput cdc_ether venus_dec venus_enc usbnet videobuf2_dma_sg videobuf2_memops hci_uart btqca bluetooth r8152 mii ath10k_snoc venus_core ath10k_core v4l2_mem2mem videobuf2_v4l2 videobuf2_common ath mac80211 ecdh_generic qcom_q6v5_mss lzo lzo_compress qcom_q6v5_adsp qcom_common qcom_q6v5 zram bridge stp llc ipt_MASQUERADE fuse snd_seq_dummy snd_seq snd_seq_device cfg80211 joydev
[  338.158192] CPU: 4 PID: 3235 Comm: chrome Tainted: G        W         4.19.0 #2
[  338.165700] Hardware name: Google Cheza (rev1) (DT)
[  338.170720] pstate: 80400009 (Nzcv daif +PAN -UAO)
[  338.175660] pc : drm_mm_insert_node_in_range+0xfc/0x348
[  338.181035] lr : drm_mm_insert_node_in_range+0x24/0x348
[  338.186407] sp : ffffff8013033b30
[  338.189816] x29: ffffff8013033bd0 x28: ffffff8008591894
[  338.195275] x27: 0000000000000010 x26: 0000000000000000
[  338.200734] x25: 0000000000000000 x24: ffffffffffffffff
[  338.206194] x23: 0000000000000000 x22: ffffffc0f48b7e08
[  338.211656] x21: 0000000000000000 x20: 000000000000005d
[  338.217118] x19: 0000000000000000 x18: 0000000000000000
[  338.222581] x17: 0000000000000000 x16: 0000000000000000
[  338.228046] x15: 0000000000000000 x14: 0000000000000000
[  338.233511] x13: 0000000000000001 x12: ffffffc0b1da7200
[  338.238978] x11: 0000000000000010 x10: 0000000000000010
[  338.244437] x9 : 0000000000000008 x8 : 0000400000000000
[  338.249898] x7 : 0000000000000000 x6 : ffffffffffffffff
[  338.255361] x5 : 0000000000000000 x4 : 0000000000000000
[  338.260823] x3 : 0000000000000000 x2 : 000000000000005d
[  338.266285] x1 : ffffffc0b1da7100 x0 : ffffffc0b0215800
[  338.271748] Process chrome (pid: 3235, stack limit = 0x000000000900f416)
[  338.278628] Call trace:
[  338.281151]  drm_mm_insert_node_in_range+0xfc/0x348
[  338.286168]  msm_gem_map_vma+0x60/0xdc
[  338.290022]  msm_gem_get_iova+0xb4/0xf4
[  338.293967]  msm_ioctl_gem_info+0x90/0xdc
[  338.298089]  drm_ioctl_kernel+0xa8/0xe8
[  338.302043]  drm_ioctl+0x218/0x384
[  338.305547]  drm_compat_ioctl+0xd8/0xe8
[  338.309503]  __arm64_compat_sys_ioctl+0x134/0x20c
[  338.314339]  el0_svc_common+0xa0/0xf0
[  338.318108]  el0_svc_compat_handler+0x2c/0x38
[  338.322588]  el0_svc_compat+0x8/0x18
[  338.326274] Code: f94066c8 aa1f03e0 321d03e9 321c03ea (f9401d0b)
[  338.332538] ---[ end trace 5c09e60869887d87 ]---
[  338.354633] Kernel panic - not syncing: Fatal exception
[  338.360018] SMP: stopping secondary CPUs
[  338.364179] Kernel Offset: disabled
[  338.367779] CPU features: 0x0,22802a18
[  338.371643] Memory Limit: none
------

 drivers/gpu/drm/drm_prime.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 231e3f6d5f41..0d9b1c43523a 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -945,7 +945,7 @@ int drm_prime_sg_to_page_addr_arrays(struct sg_table *sgt, struct page **pages,
 
 	index = 0;
 	for_each_sg(sgt->sgl, sg, sgt->nents, count) {
-		len = sg->length;
+		len = sg_dma_length(sg);
 		page = sg_page(sg);
 		addr = sg_dma_address(sg);
 
-- 
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