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

[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--

Seems like syscall_enter_from_user_mode() clobber regs->a0.


Björn