Hi,
vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP;vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);}Totally unrelated discussion around HMM lead me to a bit a chase, and realizing that we probably want a
WARN_ON(!(vma->vm_flags & VM_SPECIAL));here, to make sure drivers set at least one of the "this is a special vma, don't try to treat it like pagecache/anon memory". Just to be on the safe side. Maybe we also want to keep the entire vma->vm_flags assignment in the common code, but at least the WARN_ON would be a good check I think. Maybe also check for VM_DONTEXPAND while at it
Hmm. VM_SPECIAL is this:
#define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_PFNMAP | VM_MIXEDMAP)
Requiring VM_DONTEXPAND makes sense for sure. Dunno about the other ones. For drm_gem_vram_helper VM_IO + VM_PFNMAP are needed.
But we also have drm_gem_shmem_helper which backs objects with normal pages. In fact drm_gem_shmem_mmap does this:
/* VM_PFNMAP was set by drm_gem_mmap() */ vma->vm_flags &= ~VM_PFNMAP; vma->vm_flags |= VM_MIXEDMAP;
include/linux/mm.h isn't very helpful in explaining how VM_MIXEDMAP should be used, only saying can be both "struct page" and pfnmap, so I'm not sure why VM_MIXEDMAP is set here, it should always be "struct page" for shmem, no?
cheers, Gerd