Am 09.07.21 um 21:31 schrieb Felix Kuehling:
On 2021-07-09 2:38 a.m., Christian König wrote:
Am 08.07.21 um 21:36 schrieb Alex Deucher:
From: Felix Kuehling Felix.Kuehling@amd.com
KFD Thunk maps invisible VRAM BOs with PROT_NONE, MAP_PRIVATE. is_cow_mapping returns true for these mappings. Add a check for vm_flags & VM_WRITE to avoid mmap failures on private read-only or PROT_NONE mappings.
I'm pretty sure that this is not working as expected.
Not sure what you mean. Debugger access to the memory through the PROT_NONE VMAs is definitely working, with both ptrace and /proc/<pid>/mem.
Fixes: f91142c62161 ("drm/ttm: nuke VM_MIXEDMAP on BO mappings v3") Signed-off-by: Felix Kuehling Felix.Kuehling@amd.com Signed-off-by: Alex Deucher alexander.deucher@amd.com
drivers/gpu/drm/ttm/ttm_bo_vm.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c index f56be5bc0861..a75e90c7d4aa 100644 --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c @@ -552,7 +552,7 @@ static const struct vm_operations_struct ttm_bo_vm_ops = { int ttm_bo_mmap_obj(struct vm_area_struct *vma, struct ttm_buffer_object *bo) { /* Enforce no COW since would have really strange behavior with it. */ - if (is_cow_mapping(vma->vm_flags)) + if (is_cow_mapping(vma->vm_flags) && (vma->vm_flags & VM_WRITE))
is_cow_mapping() already checks for VM_MAYWRITE, so this here shouldn't be necessary.
AFAICT, VM_MAYWRITE is not based on the PROT_... bits used to create the VMA, but based on the permissions of the file. So as long as the render node is writable, VM_MAYWRITE is set for all VMAs that map it.
I would agree that it's probably a bad idea for the Thunk to map these VMAs with MAP_PRIVATE. We can try changing the Thunk to use MAP_SHARED for these PROT_NONE mappings. But that doesn't change the fact that this kernel patch broke existing usermode.
Yeah, but see the discussion around MAP_PRIVATE and COW regarding this. What Thunk did here was a really bad idea.
I think we have only two options here: 1. Accept the breakage of thunk. 2. Add a workaround in amdgpu/amdkfd to force MAP_PRIVATE into MAP_SHARED in the kernel.
Regards, Christian.
Regards, Felix
Christian.
return -EINVAL; ttm_bo_get(bo);