Re: [PATCH v3 00/13] Introduce sv48 support without relocatable kernel

[Alexandre Ghiti <alexandre.ghiti@canonical.com>]

On Thu, Jan 20, 2022 at 8:30 AM Alexandre Ghiti
<alexandre.ghiti@canonical.com> wrote:
>
> On Thu, Jan 20, 2022 at 5:18 AM Palmer Dabbelt <palmer@dabbelt.com> wrote:
> >
> > On Mon, 06 Dec 2021 02:46:44 PST (-0800), alexandre.ghiti@canonical.com wrote:
> > > * Please note notable changes in memory layouts and kasan population *
> > >
> > > This patchset allows to have a single kernel for sv39 and sv48 without
> > > being relocatable.
> > >
> > > The idea comes from Arnd Bergmann who suggested to do the same as x86,
> > > that is mapping the kernel to the end of the address space, which allows
> > > the kernel to be linked at the same address for both sv39 and sv48 and
> > > then does not require to be relocated at runtime.
> > >
> > > This implements sv48 support at runtime. The kernel will try to
> > > boot with 4-level page table and will fallback to 3-level if the HW does not
> > > support it. Folding the 4th level into a 3-level page table has almost no
> > > cost at runtime.
> > >
> > > Note that kasan region had to be moved to the end of the address space
> > > since its location must be known at compile-time and then be valid for
> > > both sv39 and sv48 (and sv57 that is coming).
> > >
> > > Tested on:
> > >   - qemu rv64 sv39: OK
> > >   - qemu rv64 sv48: OK
> > >   - qemu rv64 sv39 + kasan: OK
> > >   - qemu rv64 sv48 + kasan: OK
> > >   - qemu rv32: OK
> > >
> > > Changes in v3:
> > >   - Fix SZ_1T, thanks to Atish
> > >   - Fix warning create_pud_mapping, thanks to Atish
> > >   - Fix k210 nommu build, thanks to Atish
> > >   - Fix wrong rebase as noted by Samuel
> > >   - * Downgrade to sv39 is only possible if !KASAN (see commit changelog) *
> > >   - * Move KASAN next to the kernel: virtual layouts changed and kasan population *
> > >
> > > Changes in v2:
> > >   - Rebase onto for-next
> > >   - Fix KASAN
> > >   - Fix stack canary
> > >   - Get completely rid of MAXPHYSMEM configs
> > >   - Add documentation
> > >
> > > Alexandre Ghiti (13):
> > >   riscv: Move KASAN mapping next to the kernel mapping
> > >   riscv: Split early kasan mapping to prepare sv48 introduction
> > >   riscv: Introduce functions to switch pt_ops
> > >   riscv: Allow to dynamically define VA_BITS
> > >   riscv: Get rid of MAXPHYSMEM configs
> > >   asm-generic: Prepare for riscv use of pud_alloc_one and pud_free
> > >   riscv: Implement sv48 support
> > >   riscv: Use pgtable_l4_enabled to output mmu_type in cpuinfo
> > >   riscv: Explicit comment about user virtual address space size
> > >   riscv: Improve virtual kernel memory layout dump
> > >   Documentation: riscv: Add sv48 description to VM layout
> > >   riscv: Initialize thread pointer before calling C functions
> > >   riscv: Allow user to downgrade to sv39 when hw supports sv48 if !KASAN
> > >
> > >  Documentation/riscv/vm-layout.rst             |  48 ++-
> > >  arch/riscv/Kconfig                            |  37 +-
> > >  arch/riscv/configs/nommu_k210_defconfig       |   1 -
> > >  .../riscv/configs/nommu_k210_sdcard_defconfig |   1 -
> > >  arch/riscv/configs/nommu_virt_defconfig       |   1 -
> > >  arch/riscv/include/asm/csr.h                  |   3 +-
> > >  arch/riscv/include/asm/fixmap.h               |   1
> > >  arch/riscv/include/asm/kasan.h                |  11 +-
> > >  arch/riscv/include/asm/page.h                 |  20 +-
> > >  arch/riscv/include/asm/pgalloc.h              |  40 ++
> > >  arch/riscv/include/asm/pgtable-64.h           | 108 ++++-
> > >  arch/riscv/include/asm/pgtable.h              |  47 +-
> > >  arch/riscv/include/asm/sparsemem.h            |   6 +-
> > >  arch/riscv/kernel/cpu.c                       |  23 +-
> > >  arch/riscv/kernel/head.S                      |   4 +-
> > >  arch/riscv/mm/context.c                       |   4 +-
> > >  arch/riscv/mm/init.c                          | 408 ++++++++++++++----
> > >  arch/riscv/mm/kasan_init.c                    | 250 ++++++++---
> > >  drivers/firmware/efi/libstub/efi-stub.c       |   2
> > >  drivers/pci/controller/pci-xgene.c            |   2 +-
> > >  include/asm-generic/pgalloc.h                 |  24 +-
> > >  include/linux/sizes.h                         |   1
> > >  22 files changed, 833 insertions(+), 209 deletions(-)
> >
> > Sorry this took a while.  This is on for-next, with a bit of juggling: a
> > handful of trivial fixes for configs that were failing to build/boot and
> > some merge issues.  I also pulled out that MAXPHYSMEM fix to the top, so
> > it'd be easier to backport.  This is bigger than something I'd normally like to
> > take late in the cycle, but given there's a lot of cleanups, likely some fixes,
> > and it looks like folks have been testing this I'm just going to go with it.
> >
>
> Yes yes yes! That's fantastic news :)
>
> > Let me know if there's any issues with the merge, it was a bit hairy.
> > Probably best to just send along a fixup patch at this point.
>
> I'm going to take a look at that now, and I'll fix anything that comes
> up quickly :)

I see in for-next that you did not take the following patches:

  riscv: Improve virtual kernel memory layout dump
  Documentation: riscv: Add sv48 description to VM layout
  riscv: Initialize thread pointer before calling C functions
  riscv: Allow user to downgrade to sv39 when hw supports sv48 if !KASAN

I'm not sure this was your intention. If it was, I believe that at
least the first 2 patches are needed in this series, the 3rd one is a
useful fix and we can discuss the 4th if that's an issue for you.

I tested for-next on both sv39 and sv48 successfully, I took a glance
at the code and noticed you fixed the PTRS_PER_PGD error, thanks for
that. Otherwise nothing obvious has popped.

Thanks again,

Alex

>
> Thanks!
>
> Alex
>
> >
> > Thanks!