Re: [PATCH v5 21/38] uprobes: remove VM_IO, set VM_MIXEDMAP for mapped kernel pages

These are not MMIO pages so VMA_IO_BIT is an inappropriate flag to set.

Instead, set them VMA_MIXEDMAP_BIT as they are kernel mappings and this is
the appropriate flag to set for those.

This provides the semantics required - no VMA merging is permitted, but
does not prevent GUP.

However this has no meaningful impact as these are refcounted and thus can
be GUPed.

A previous commit already prevented __mm_populate() from being invoked on
XOL areas, which VMA_IO_BIT was previously relied upon to do, so that is no
longer required.

Both VMAs set a VMA name, so always_dump_vma() returns true before
vma_dump_size() reaches its VMA_IO_BIT check, and thus there is no change
in core dump behaviour.

Change this for both the core xol_add_vma() function and the x86-specific
get_uprobe_trampoline() function.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
---
 arch/x86/kernel/uprobes.c | 2 +-
 kernel/events/uprobes.c   | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/uprobes.c b/arch/x86/kernel/uprobes.c
index 65a2de82ecd2..0f60c0d076b6 100644
--- a/arch/x86/kernel/uprobes.c
+++ b/arch/x86/kernel/uprobes.c

@@ -715,7 +715,7 @@ static struct vm_area_struct *get_uprobe_trampoline(struct mm_struct *mm, unsign
 
 	*new_mapping = true;
 	return _install_special_mapping(mm, vaddr, PAGE_SIZE,
-				VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_IO,
+				VM_READ|VM_EXEC|VM_MAYEXEC|VM_MAYREAD|VM_MIXEDMAP,
 				&tramp_mapping);