Re: [PATCH] drm/amdgpu: fix an underflow on non-4KB-page systems
From: Christian König
Date: Mon Mar 29 2021 - 15:37:32 EST
Am 29.03.21 um 21:27 schrieb Xi Ruoyao:
Hi Christian,
I don't think there is any constraint implemented to ensure `num_entries %
AMDGPU_GPU_PAGES_IN_CPU_PAGE == 0`. For example, in `amdgpu_vm_bo_map()`:
/* validate the parameters */
if (saddr & AMDGPU_GPU_PAGE_MASK || offset & AMDGPU_GPU_PAGE_MASK ||
size == 0 || size & AMDGPU_GPU_PAGE_MASK)
return -EINVAL;
/* snip */
saddr /= AMDGPU_GPU_PAGE_SIZE;
eaddr /= AMDGPU_GPU_PAGE_SIZE;
/* snip */
mapping->start = saddr;
mapping->last = eaddr;
If we really want to ensure (mapping->last - mapping->start + 1) %
AMDGPU_GPU_PAGES_IN_CPU_PAGE == 0, then we should replace "AMDGPU_GPU_PAGE_MASK"
in "validate the parameters" with "PAGE_MASK".
Yeah, good point.
I tried it and it broke userspace: Xorg startup fails with EINVAL with this
change.
Well in theory it is possible that we always fill the GPUVM on a 4k
basis while the native page size of the CPU is larger. Let me double
check the code.
BTW: What code base are you based on? The code your post here is quite
outdated.
Christian.
On 2021-03-30 02:30 +0800, Xi Ruoyao wrote:
On 2021-03-30 02:21 +0800, Xi Ruoyao wrote:
On 2021-03-29 20:10 +0200, Christian König wrote:
You need to identify the root cause of this, most likely start or last
are not a multiple of AMDGPU_GPU_PAGES_IN_CPU_PAGE.
I printk'ed the value of start & last, they are all a multiple of 4
(AMDGPU_GPU_PAGES_IN_CPU_PAGE).
However... `num_entries = last - start + 1` so it became some irrational
thing... Either this line is wrong, or someone called
amdgpu_vm_bo_update_mapping with [start, last) instead of [start, last], which
is unexpected.
I added BUG_ON(num_entries % AMDGPU_GPU_PAGES_IN_CPU_PAGE != 0), get:
Mar 30 02:28:27 xry111-A1901 kernel: [<ffffffff83c90750>]
amdgpu_vm_bo_update_mapping.constprop.0+0x218/0xae8
Mar 30 02:28:27 xry111-A1901 kernel: [<ffffffff83c922b8>]
amdgpu_vm_bo_update+0x270/0x4c0
Mar 30 02:28:27 xry111-A1901 kernel: [<ffffffff83c823ec>]
amdgpu_gem_va_ioctl+0x40c/0x430
Mar 30 02:28:27 xry111-A1901 kernel: [<ffffffff83c1cae4>]
drm_ioctl_kernel+0xcc/0x120
Mar 30 02:28:27 xry111-A1901 kernel: [<ffffffff83c1cfd8>]
drm_ioctl+0x220/0x408
Mar 30 02:28:27 xry111-A1901 kernel: [<ffffffff83c5ea48>]
amdgpu_drm_ioctl+0x58/0x98
Mar 30 02:28:27 xry111-A1901 kernel: [<ffffffff838feac4>] sys_ioctl+0xcc/0xe8
Mar 30 02:28:27 xry111-A1901 kernel: [<ffffffff836e74f0>]
syscall_common+0x34/0x58
BugLink: https://gitlab.freedesktop.org/drm/amd/-/issues/1549
Fixes: a39f2a8d7066 ("drm/amdgpu: nuke amdgpu_vm_bo_split_mapping v2")
Reported-by: Xi Ruoyao <xry111@xxxxxxxxxxxxxxxx>
Reported-by: Dan Horák <dan@xxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Xi Ruoyao <xry111@xxxxxxxxxxxxxxxx>
---
drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index ad91c0c3c423..cee0cc9c8085 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -1707,7 +1707,7 @@ static int amdgpu_vm_bo_update_mapping(struct
amdgpu_device *adev,
}
start = tmp;
- } while (unlikely(start != last + 1));
+ } while (unlikely(start < last + 1));
r = vm->update_funcs->commit(¶ms, fence);
base-commit: a5e13c6df0e41702d2b2c77c8ad41677ebb065b3