On Fri, 5 Jan 2018 10:58:11 +0800 Chao Fan <fanc.f...@cn.fujitsu.com> wrote:
> On Thu, Jan 04, 2018 at 06:30:57PM +0800, Baoquan He wrote: > >On 01/04/18 at 04:02pm, Chao Fan wrote: > >> In current code, kaslr may choose the memory region in movable > >> nodes to extract kernel, which will make the nodes can't be hot-removed. > >> To solve it, we can specify the memory region in immovable node. > >> Create immovable_mem to store the regions in immovable_mem, where should > >> be chosen by kaslr. > >> > >> Also change the "handle_mem_memmap" to "handle_mem_filter", since > >> it will not only handle memmap parameter now. > >> Since "immovable_mem=" only works with "movable_node", so "immovable_mem=" > >> doesn't work alone. If specify "movable_node" without "immovable_mem=", > >> disable KASLR. > >> > >> Multiple regions can be specified, comma delimited. > >> Considering the usage of memory, only support for 4 regions. > >> 4 regions contains 2 nodes at least, enough for kernel to extract. > >> > >> Signed-off-by: Chao Fan <fanc.f...@cn.fujitsu.com> > > > >Hi Chao, > > > >Thanks for your effort on this issue. > > > >Luiz told me they met a hugetlb issue when kaslr enabled on kvm guest. > >Please check the below bug information. There's only one available > >position which hugepage can use to allocate. In this case, if we have a > >generic parameter to tell kernel where we can randomize into, this > >hugepage issue can be solved. We can restrict kernel to randomize beyond > >[0x40000000, 0x7fffffff]. Not sure if your immovable_mem=nn[KMG]@ss[KMG] > >can be adjusted to do this. I am hesitating on whether we should change > >this or not. > > > > Hi Baoquan, Luiz, > > In my personal understanding, there is only one region, > [0x40000000, 0x7fffffff] suitable for the 1G page, so we should avoid > kaslr to choose this region, right? For a guest configured with 4GB of memory with the device configuration we're using yes. > If my understanding is right, I think it's more similar with mem_avoid. > Because we specify where KASLR *choose* in "immovable_mem=", we specify > where KASLR *avoid* in "mem_avoid". > So I wonder if it's OK to expand mem_avoid, and add a member like > MEM_AVOID_HUGEPAGE in "enum mem_avoid_index". > But there is a disadvantage, we can only specify the limited regions. Not requiring new command-line options would be great for users, but I'm not sure it's possible to use mem_avoid because I guess the free area may vary depending on amount of memory, devices, etc. > Luiz, I am not familiar with HUGE PAGE, I wonder how many 1G HUGE pages > does system need in general? We may need to limit it in 2, or 4. I don't think it's possible to impose a limit. But the case we've been discussing in this thread it the case that has the greater impact: a guest with 4GB of memory which always has 1GB page with nokaslr, but may not have any 1GB page without nokaslr.