[PATCH -next V17 4/7] riscv: entry: Convert to generic entry

[Guo Ren]

On Sun, Apr 2, 2023 at 2:41 AM Björn Töpel <bjorn at kernel.org> wrote:
>
> Heiko Stübner <heiko at sntech.de> writes:
>
> > Am Samstag, 1. April 2023, 16:58:01 CEST schrieb Björn Töpel:
> >> Björn Töpel <bjorn at kernel.org> writes:
> >>
> >> > (Narrowing the Cc list.)
> >> >
> >> > Björn Töpel <bjorn at kernel.org> writes:
> >> >
> >> >>>> > > > This has unfortunately broken booting my usual NFS rootfs on both my D1
> >> >>>> > > > and Icicle. It's one of the Fedora images from David, I think this one:
> >> >>>> > > > http://fedora.riscv.rocks/kojifiles/work/tasks/3933/1313933/
> >> >>>> > > >
> >> >>>> > > > It gets pretty far into things, it's once systemd is operational that
> >> >>>> > > > things go pear shaped:
> >> >>>> > >
> >> >>>> > > Shoulda said, can share the full logs if required of course, but they're
> >> >>>> > > quite verbose cos systemd etc.
> >> >>>> >
> >> >>>> > I was just investigating the same thing just now. So that saves me some
> >> >>>> > tracking down the culprit :-) .
> >> >>>> >
> >> >>>> > My main qemu is living as a "board" in my boardfarm (also doing nfsroot)
> >> >>>> > as well as my d1 nezha with nfsroot was affected.
> >> >>>> Can you reproduce it with qemu? Could give me some tips and let me
> >> >>>> reproduce it on qemu?
> >> >>
> >> >> FWIW, I'm getting the systemd issue w/o NFS, on a regular 9p virtfs.
> >> >>
> >> >> | $ sudo mmdebstrap --architecture=riscv64 lunar rv-rootfs http://ports.ubuntu.com
> >> >>
> >> >> and the rootfs qemu config:
> >> >>  |  -fsdev local,id=root,path=/path/to/rv-rootfs/,security_model=none \
> >> >>  |  -device virtio-9p-pci,fsdev=root,mount_tag=/dev/root \
> >> >>  |  -append "root=/dev/root rw rootfstype=9p rootflags=version=9p2000.L,trans=virtio,cache=mmap,access=any security=none earlycon console=tty0 console=ttyS0"
> >> >
> >> > I took a couple of different versions of the series for a spin, and for
> >> > me it stops working between these versions.
> >> >
> >> > $ git fetch https://github.com/guoren83/linux.git generic_entry_v12:ge-v12
> >> > $ git fetch https://github.com/guoren83/linux.git generic_entry_v13:g2-v13
> >> >
> >> > v12 is happy with systemd, v13 is not.
> >>
> >> Hmm, this patch seems to resolve the issue for me:
> >>
> >> --8<--
> >> diff --git a/arch/riscv/kernel/traps.c b/arch/riscv/kernel/traps.c
> >> index       1f4e37be7eb3..8c258b78c925 100644
> >> --- a/arch/riscv/kernel/traps.c
> >> +++ b/arch/riscv/kernel/traps.c
> >> @@ -270,11 +270,11 @@ asmlinkage __visible __trap_section void do_trap_ecall_u(struct pt_regs *regs)
> >>         if (user_mode(regs)) {
> >>                 ulong syscall = regs->a7;
> >>
> >> -               syscall = syscall_enter_from_user_mode(regs, syscall);
> >> -
> >>                 regs->epc += 4;
> >>                 regs->orig_a0 = regs->a0;
> >>
> >> +               syscall = syscall_enter_from_user_mode(regs, syscall);
> >> +
> >>                 if (syscall < NR_syscalls)
> >>                         syscall_handler(regs, syscall);
> >>                 else
> >> -->8--
> >
> > Woohoo, thanks for tracking that down. This change makes both my
> > Qemu and D1-Nezha boot again.
> >
> >> Seems like syscall_enter_from_user_mode() clobber regs->a0.
> >
> > With a0 also being the return value in the calling conventions (and being
> > the syscall value here), I guess that could be somehow expected and thus
> > as your patch does, the a0 value should be saved first I guess?
> >
> > An it looks like Loonarch also does save a0 before calling
> > syscall_enter_from_user_mode() [0]
> >
> > Reviewed-by: Heiko Stuebner <heiko.stuebner at vrull.eu>
> > Tested-by: Heiko Stuebner <heiko.stuebner at vrull.eu>
>
> Cool, and thanks for testing/verifying! I'll cook a proper patch on
> Monday.
Just ping gently :) Have you done it?

>
>
> Björn
>
>


-- 
Best Regards
 Guo Ren