Hi Luiz, On 01/04/18 at 11:21am, Luiz Capitulino wrote: > Having a generic kaslr parameter to control where the kernel is extracted > is one solution for this problem. > > The general problem statement is that KASLR may break some kernel features > depending on where the kernel is extracted. Two examples are hot-plugged > memory (this series) and 1GB HugeTLB pages. > > The 1GB HugeTLB page issue is not specific to KVM guests. It just happens > that there's a bunch of people running guests with up to 5GB of memory and > with that amount of memory you have one or two 1GB pages and is easier for > KASLR to extract the kernel into a 1GB region and split a 1GB page. So, > you may not get any 1GB pages at all when this happens. However, I can also > reproduce this on bare-metal with lots of memory where I can loose a 1GB > page from time to time. > > Having a kaslr_range= parameter solves both issues, but two major drawbacks > is that it breaks existing setups and I guess users will have a very hard > time choosing good ranges. > > Another idea would be to have a CONFIG_KASLR_RANGES, where each arch > could have a list of ranges known to contain holes and/or immovable > memory and only extract the kernel into those ranges.
If add CONFIG_KASLR_RANGES, then a distro like RHEL will have this range always, whether people need hugetlb or not. So in this case, what range do we need to avoid? Only [1G, 2G]? Thanks Baoquan
