Messages in this thread | | | Subject | Correct way to access the physmap? - Was: Re: [PATCH 7/9] Pmalloc Rare Write: modify selected pools | From | Igor Stoppa <> | Date | Fri, 4 May 2018 01:52:29 +0400 |
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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
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