On Mon, Sep 12, 2022 at 4:23 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: > > On Sun, 11 Sep 2022 09:59:20 +0000 Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> wrote: > > > From: Pasha Tatashin <tatashin@xxxxxxxxxx> > > > > Page table check when detects errors panics the kernel. Let instead, > > print a warning, and panic only when specifically requested via kernel > > parameter: > > > > page_table_check=panic > > > > The discussion about using panic vs. warn is here: > > https://lore.kernel.org/linux-mm/20220902232732.12358-1-rick.p.edgecombe@xxxxxxxxx > > The changelog doesn't actually describe the reason for making this > change. Somebody obviously wants pagetable check errors to no longer > panic the kernel, but why?? (The same can be said of the [2/3] > changelog). This came from the discussion listed above. There seems to be a consensus that we should reduce the number of BUG_ON() in the kernel, and replace them with WARN_ON_ONCE() when possible to recover. In the case of page_table_check we can recover, but for some it may be unsafe because of security implications. Therefore, I would like to keep an option of being able to panic only because of page table check errors, but not keeping it enabled by default. I will add more info to the commit message. > > Also, should we be changing the default? People who like the panic > will get a big surprise when they find out that they should have added > a kernel parameter to get the old behaviour back. It would be less > disruptive to default to panic unless page_table_check=warn was added. I was thinking about this as well. I decided to change the default: the old users will still get a warning, but going forward we will be inline with the rest of the kernel: warn on by default, and optionally panic. > > If there's a solid reason for changing the default, it should be > changelogged. And if that reason is generally agreed to, perhaps the > kernel should print a warning at boot if neither page_table_check=panic > nor page_table_check=warn were provided. To tell people that the > default has been changed. I am not sure that is needed, and when do we remove that extra boot message? This is a relatively new feature, and existing users would still get an ugly warning about incorrect page table mappings. Thank you, Pasha > >
