On 24/04/18 15:50, Matthew Wilcox wrote:
On Mon, Apr 23, 2018 at 04:54:56PM +0400, Igor Stoppa wrote:
While the vanilla version of pmalloc provides support for permanently
transitioning between writable and read-only of a memory pool, this
patch seeks to support a separate class of data, which would still
benefit from write protection, most of the time, but it still needs to
be modifiable. Maybe very seldom, but still cannot be permanently marked
as read-only.
This seems like a horrible idea that basically makes this feature useless.
I would say the right way to do this is to have:
struct modifiable_data {
struct immutable_data *d;
...
};
Then allocate a new pool, change d and destroy the old pool.
At the end of the summit, we agreed that I would go through the physmap.
But I'm not sure of what is the correct way to access it :-/
Starting from a vmalloc address, say:
int *i = vmalloc(sizeof(int));
I can get its linear counterpart:
int *j = page_to_virt(vmalloc_to_page(i));
and the physical address:
int *k = virt_to_phys(j);
But how do I get to the physmap?
I did not find much about it, apart from papers that talk about specific
hardcoded addresses, but I would expect that if there is any hardcoded
constant, by now, it's hidden behind some macro.
What I have verified, so far, at least on qemu x86_64, is that
protecting "i" will also make "j" unwritable.
--
igor
