Messages in this thread | | | Date | Sun, 7 Jun 2020 18:29:32 +0530 | From | afzal mohammed <> | Subject | ARM: vmsplit 4g/4g |
| |
Hi,
On Sat, May 16, 2020 at 09:35:57AM +0200, Arnd Bergmann wrote: > On Sat, May 16, 2020 at 8:06 AM afzal mohammed <afzal.mohd.ma@gmail.com> wrote:
> > Okay, so the conclusion i take is, > > 1. VMSPLIT 4G/4G have to live alongside highmem > > 2. For user space copy, do pinning followed by kmap
> Right, though kmap_atomic() should be sufficient here > because it is always a short-lived mapping.
get_user_pages_fast() followed by kmap_atomic() & then memcpy() seems to work in principle for user copy.
Verified in a crude way by pointing TTBR0 to a location that has user pgd's cleared upon entry to copy_to_user() & restoring TTBR0 to earlier value after user copying was done and ensuring boot.
Meanwhile more testing w/ kernel static mapping in vmalloc space revealed a major issue, w/ LPAE it was not booting. There were issues related to pmd handling, w/ !LPAE those issues were not present as pmd is in effect equivalent to pgd. The issues has been fixed, though now LPAE boots, but feel a kind of fragile, will probably have to revisit it.
Regards afzal
| |