Messages in this thread | | | Date | Thu, 14 May 2020 17:25:35 +0100 | From | Russell King - ARM Linux admin <> | Subject | Re: ARM: static kernel in vmalloc space |
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On Thu, May 14, 2020 at 02:41:11PM +0200, Arnd Bergmann wrote: > On Thu, May 14, 2020 at 1:18 PM afzal mohammed <afzal.mohd.ma@gmail.com> wrote: > > On Tue, May 12, 2020 at 09:49:59PM +0200, Arnd Bergmann wrote: > > > > > Any idea which bit you want to try next? > > > > My plan has been to next post patches for the static kernel migration > > to vmalloc space (currently the code is rigid, taking easy route > > wherever possible & not of high quality) as that feature has an > > independent existence & adds value by itself. And then start working > > on other steps towards VMSPLIT_4G_4G. > > > > Now that you mentioned about other things, i will slowly start those > > as well. > > Sounds good. > > > > Creating a raw_copy_{from,to}_user() > > > based on get_user_pages()/kmap_atomic()/memcpy() is probably a good > > > next thing to do. I think it can be done one page at a time with only > > > checking for > > > get_fs(), access_ok(), and page permissions, while get_user()/put_user() > > > need to handle a few more corner cases. > > > > Before starting w/ other things, i would like to align on the high > > level design, > > > > My understanding (mostly based on your comments) as follows, > > (i currently do not have a firm grip over these things, hope to have > > it once started w/ the implementation) > > > > 1. SoC w/ LPAE > > 2. TTBR1 (top 256MB) for static kernel, modules, io mappings, vmalloc, > > kmap, fixmap & vectors > > Right, these kind of go together because pre-LPAE cannot do the > same TTBR1 split, and they more frequently have conflicting > static mappings. > > It's clearly possible to do something very similar for older chips > (v6 or v7 without LPAE, possibly even v5), it just gets harder > while providing less benefit.
Forget about doing this for anything without a PIPT cache - or you're going to end up having to flush the data cache each time you enter or exit the kernel.
-- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line in suburbia: sync at 10.2Mbps down 587kbps up
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