On Wed, 2018-12-12 at 06:30 +0000, Nadav Amit wrote:

quoted

On Dec 11, 2018, at 4:03 PM, Rick Edgecombe [off-list ref]
wrote:

This adds a more efficient x86 architecture specific implementation of
arch_vunmap, that can free any type of special permission memory with only 1
TLB
flush.

In order to enable this, _set_pages_p and _set_pages_np are made non-static
and
renamed set_pages_p_noflush and set_pages_np_noflush to better communicate
their different (non-flushing) behavior from the rest of the set_pages_*
functions.

The method for doing this with only 1 TLB flush was suggested by Andy
Lutomirski.

[snip]

quoted

+	/*
+	 * If the vm being freed has security sensitive capabilities such as
+	 * executable we need to make sure there is no W window on the directmap
+	 * before removing the X in the TLB. So we set not present first so we
+	 * can flush without any other CPU picking up the mapping. Then we reset
+	 * RW+P without a flush, since NP prevented it from being cached by
+	 * other cpus.
+	 */
+	set_area_direct_np(area);
+	vm_unmap_aliases();

Does vm_unmap_aliases() flush in the TLB the direct mapping range as well? I
can only find the flush of the vmalloc range.

Hmmm. It should usually (I tested), but now I wonder if there are cases where it
doesn't and it could depend on architecture as well. I'll have to trace through
this to verify, thanks.

Rick