Re: [PATCH v7 00/13] riscv: support for Svpbmt and D1 memory types

Heiko Stübner
2022-03-08T11:56:34Z

Hi Palmer,

Am Dienstag, 8. März 2022, 01:47:25 CET schrieb Palmer Dabbelt:
> On Mon, 07 Mar 2022 12:52:57 PST (-0800), heiko@sntech.de wrote:
> > Svpbmt is an extension defining "Supervisor-mode: page-based memory types"
> > for things like non-cacheable pages or I/O memory pages.
> >
> >
> > So this is my 2nd try at implementing Svpbmt (and the diverging D1 memory
> > types) using the alternatives framework.
> >
> > This includes a number of changes to the alternatives mechanism itself.
> > The biggest one being the move to a more central location, as I expect
> > in the future, nearly every chip needing some sort of patching, be it
> > either for erratas or for optional features (svpbmt or others).
> >
> > Detection of the svpbmt functionality is done via Atish's isa extension
> > handling series [0] and thus does not need any dt-parsing of its own
> > anymore.
> >
> > The series also introduces support for the memory types of the D1
> > which are implemented differently to svpbmt. But when patching anyway
> > it's pretty clean to add the D1 variant via ALTERNATIVE_2 to the same
> > location.
> >
> > The only slightly bigger difference is that the "normal" type is not 0
> > as with svpbmt, so kernel patches for this PMA type need to be applied
> > even before the MMU is brought up, so the series introduces a separate
> > stage for that.
> >
> >
> > In theory this series is 3 parts:
> > - sbi cache-flush / null-ptr
>
> That first patch looks like an acceptable candidate for fixes. If
> there's a regression that manifests I'm happy to take it, but if it's
> only possible to manifest a crash with the new stuff then I'm OK just
> holding off until the merge window.

While right now only my poking around the early init via alternatives
is affected, the problem exists for everyone.

I.e. I do consider flush_icache_all() to be generic enough that we
should expect someone trying to call this in some early code-path
as well.

But any call to flush_icache_all() before sbi_init() ran will cause the
breakage that is fixed by patch1 .

So it doesn't look like any _current_ code path has that issue, but
it might be good to just pick patch1 for the next merge window
individually?

> > - alternatives improvements
> > - svpbmt+d1
> >
> > So expecially patches from the first 2 areas could be applied when
> > deemed ready, I just thought to keep it together to show-case where
> > the end-goal is and not requiring jumping between different series.
> >
> >
> > I picked the recipient list from the previous versions, hopefully
> > I didn't forget anybody.
> >
> > changes in v7:
> > - fix typo in patch1 (Atish)
> > - moved to Atish's isa-extension framework
> > - and therefore move regular boot-alternatives directly behind fill_hwcaps
> > - change T-Head errata Kconfig text (Atish)
>
> I was just poking around v6, so I have some minor comments there. None
> of those need to block merging this, but I am getting a bunch of build
> failures under allmodconfig
>
> $ make.riscv allmodconfig
> #
> # configuration written to .config
> #
> $ make.riscv mm/kasan/init.o
> SYNC include/config/auto.conf.cmd
> CALL scripts/atomic/check-atomics.sh
> CC arch/riscv/kernel/asm-offsets.s
> CALL scripts/checksyscalls.sh
> CC mm/kasan/init.o
> ./arch/riscv/include/asm/pgtable.h: Assembler messages:
> ./arch/riscv/include/asm/pgtable.h:323: Error: attempt to move .org backwards
> make[2]: *** [scripts/Makefile.build:288: mm/kasan/init.o] Error 1
> make[1]: *** [scripts/Makefile.build:550: mm/kasan] Error 2
> make: *** [Makefile:1831: mm] Error 2
>
> Unfortunately my build box just blew up so I haven't had time to confim
> this still exists on v7, but nothing's jumping out as a fix. I've put
> this on the riscv-d1 branch at kernel.org/palmer/linux, not sure exactly
> what's going on but I'm guessing one of the macros has gone off the
> rails. I'm going to look at something else (as this one at least
> depends on Atish's patches), but LMK if you've got the time to look into
> this or if I should.

Yeah, we now depend on Atish's isa-extension parsing (same for my cmo
series and some more series I saw on the list), so getting that into a
mergeable position would be really great :-)

"attempt to move .org backwards" seems to be the telltale sign of the
alternatives blocks not matching up in size. While I definitly didn't see
anything like this in my tests on qemu + d1, I'll try to investigate where
that comes from.

Heiko

> > changes in v6:
> > - rebase onto 5.17-rc1
> > - handle sbi null-ptr differently
> > - improve commit messages
> > - use riscv,mmu as property name
> >
> > changes in v5:
> > - move to use alternatives for runtime-patching
> > - add D1 variant
> >
> >
> > [0] https://lore.kernel.org/r/20220222204811.2281949-2-atishp@rivosinc.com
> >
> >
> > Heiko Stuebner (12):
> > riscv: prevent null-pointer dereference with sbi_remote_fence_i
> > riscv: integrate alternatives better into the main architecture
> > riscv: allow different stages with alternatives
> > riscv: implement module alternatives
> > riscv: implement ALTERNATIVE_2 macro
> > riscv: extend concatenated alternatives-lines to the same length
> > riscv: prevent compressed instructions in alternatives
> > riscv: move boot alternatives to after fill_hwcap
> > riscv: Fix accessing pfn bits in PTEs for non-32bit variants
> > riscv: add cpufeature handling via alternatives
> > riscv: remove FIXMAP_PAGE_IO and fall back to its default value
> > riscv: add memory-type errata for T-Head
> >
> > Wei Fu (1):
> > riscv: add RISC-V Svpbmt extension support
> >
> > arch/riscv/Kconfig.erratas | 29 +++--
> > arch/riscv/Kconfig.socs | 1 -
> > arch/riscv/Makefile | 2 +-
> > arch/riscv/errata/Makefile | 2 +-
> > arch/riscv/errata/sifive/errata.c | 17 ++-
> > arch/riscv/errata/thead/Makefile | 1 +
> > arch/riscv/errata/thead/errata.c | 85 +++++++++++++++
> > arch/riscv/include/asm/alternative-macros.h | 114 +++++++++++---------
> > arch/riscv/include/asm/alternative.h | 16 ++-
> > arch/riscv/include/asm/errata_list.h | 52 +++++++++
> > arch/riscv/include/asm/fixmap.h | 2 -
> > arch/riscv/include/asm/hwcap.h | 1 +
> > arch/riscv/include/asm/pgtable-32.h | 17 +++
> > arch/riscv/include/asm/pgtable-64.h | 79 +++++++++++++-
> > arch/riscv/include/asm/pgtable-bits.h | 10 --
> > arch/riscv/include/asm/pgtable.h | 53 +++++++--
> > arch/riscv/include/asm/vendorid_list.h | 1 +
> > arch/riscv/kernel/Makefile | 1 +
> > arch/riscv/{errata => kernel}/alternative.c | 48 +++++++--
> > arch/riscv/kernel/cpu.c | 1 +
> > arch/riscv/kernel/cpufeature.c | 80 +++++++++++++-
> > arch/riscv/kernel/module.c | 29 +++++
> > arch/riscv/kernel/sbi.c | 10 +-
> > arch/riscv/kernel/setup.c | 2 +
> > arch/riscv/kernel/smpboot.c | 4 -
> > arch/riscv/kernel/traps.c | 2 +-
> > arch/riscv/mm/init.c | 1 +
> > 27 files changed, 546 insertions(+), 114 deletions(-)
> > create mode 100644 arch/riscv/errata/thead/Makefile
> > create mode 100644 arch/riscv/errata/thead/errata.c
> > rename arch/riscv/{errata => kernel}/alternative.c (59%)
>