Date:   Fri, 18 Mar 2022 17:22:29 +0100
From:   Heiko Stübner <heiko@...ech.de>
To:     Palmer Dabbelt <palmer@...belt.com>
Cc:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        wefu@...hat.com, liush@...winnertech.com, guoren@...nel.org,
        atishp@...shpatra.org, anup@...infault.org, drew@...gleboard.org,
        Christoph Hellwig <hch@....de>, Arnd Bergmann <arnd@...db.de>,
        wens@...e.org, maxime@...no.tech, gfavor@...tanamicro.com,
        andrea.mondelli@...wei.com, behrensj@....edu, xinhaoqu@...wei.com,
        mick@....forth.gr, allen.baum@...erantotech.com,
        jscheid@...tanamicro.com, rtrauben@...il.com, samuel@...lland.org,
        cmuellner@...ux.com, philipp.tomsich@...ll.eu
Subject: Re: [PATCH v7 00/13] riscv: support for Svpbmt and D1 memory types

Hi Palmer,

Am Freitag, 18. März 2022, 04:40:23 CET schrieb Palmer Dabbelt:
> On Wed, 09 Mar 2022 14:06:55 PST (-0800), heiko@...ech.de wrote:
> > Am Dienstag, 8. März 2022, 12:56:20 CET schrieb Heiko Stübner:
> >> 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@...ech.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.
> >
> > Hmm, looking at your branch [0] it seems that you're missing
> > patch7 that introduces the no-compressed-instruction thingy
> > for alternatives.
> >
> > And missing that patch will of course cause the size issue.
> >
> > The patch has made its way to the actual mailing lists [1], so I guess
> > it "just" somehow didn't reach your inbox due to some mail hickup?
> 
> Sorry about that, I'm not sure what happened.

no worries :-) . And I also have no clue where the hickup happened
but am thankful that there is no general problem with mails.


> Unfortunately I'm now getting some even trickier failures: a handful of 
> configurations are failing very early in boot.  There doesn't seem to be 
> much pattern to the configs that fail, but at least rv32 defconfig (on 
> QEMU's virt board) is doing so.  I've tried poking around a bit and 
> can't figure out what's going on.  I'll try and look again tomorrow 
> morning.

Hmm, really strange especially as the whole thing is somewhat
limited to 64bit anyway.

I guess it would be interesting if it's in the alternative-basics
part of the svpbmt implementation.

My short try on getting a (any) rv32 kernel boot in qemu wasn't sucessful
yet, so I'll need to poke that more next week.

Heiko


> I've put my somewhat messy merged test branch at 
> kernel.org/palmer/riscv-d1-merge .  Happy to hear if you have any 
> insights, otherwise I'l give it another shot (possibly after looking at 
> some other patches, there's quite a bit of a queue for this late).
> 
> >
> >
> > Heiko
> >
> >
> > [0] https://git.kernel.org/pub/scm/linux/kernel/git/palmer/linux.git/log/?h=riscv-d1
> > [1] https://lore.kernel.org/all/20220307205310.1905628-8-heiko@sntech.de/
> >
> >
> >> > > 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%)
> >> > 
> >> 
> >> 
> 

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