[PATCH v12 00/25] Linux RISC-V AIA Support

[Anup Patel]

On Tue, Jan 30, 2024 at 11:19 PM Björn Töpel <bjorn at kernel.org> wrote:
>
> Anup Patel <apatel at ventanamicro.com> writes:
>
> > On Tue, Jan 30, 2024 at 8:18 PM Björn Töpel <bjorn at kernel.org> wrote:
> >>
> >> Björn Töpel <bjorn at kernel.org> writes:
> >>
> >> > Anup Patel <apatel at ventanamicro.com> writes:
> >> >
> >> >> On Tue, Jan 30, 2024 at 1:22 PM Björn Töpel <bjorn at kernel.org> wrote:
> >> >>>
> >> >>> Björn Töpel <bjorn at kernel.org> writes:
> >> >>>
> >> >>> > Anup Patel <apatel at ventanamicro.com> writes:
> >> >>> >
> >> >>> >> The RISC-V AIA specification is ratified as-per the RISC-V international
> >> >>> >> process. The latest ratified AIA specifcation can be found at:
> >> >>> >> https://github.com/riscv/riscv-aia/releases/download/1.0/riscv-interrupts-1.0.pdf
> >> >>> >>
> >> >>> >> At a high-level, the AIA specification adds three things:
> >> >>> >> 1) AIA CSRs
> >> >>> >>    - Improved local interrupt support
> >> >>> >> 2) Incoming Message Signaled Interrupt Controller (IMSIC)
> >> >>> >>    - Per-HART MSI controller
> >> >>> >>    - Support MSI virtualization
> >> >>> >>    - Support IPI along with virtualization
> >> >>> >> 3) Advanced Platform-Level Interrupt Controller (APLIC)
> >> >>> >>    - Wired interrupt controller
> >> >>> >>    - In MSI-mode, converts wired interrupt into MSIs (i.e. MSI generator)
> >> >>> >>    - In Direct-mode, injects external interrupts directly into HARTs
> >> >>> >>
> >> >>> >> For an overview of the AIA specification, refer the AIA virtualization
> >> >>> >> talk at KVM Forum 2022:
> >> >>> >> https://static.sched.com/hosted_files/kvmforum2022/a1/AIA_Virtualization_in_KVM_RISCV_final.pdf
> >> >>> >> https://www.youtube.com/watch?v=r071dL8Z0yo
> >> >>> >>
> >> >>> >> To test this series, use QEMU v7.2 (or higher) and OpenSBI v1.2 (or higher).
> >> >>> >>
> >> >>> >> These patches can also be found in the riscv_aia_v12 branch at:
> >> >>> >> https://github.com/avpatel/linux.git
> >> >>> >>
> >> >>> >> Changes since v11:
> >> >>> >>  - Rebased on Linux-6.8-rc1
> >> >>> >>  - Included kernel/irq related patches from "genirq, irqchip: Convert ARM
> >> >>> >>    MSI handling to per device MSI domains" series by Thomas.
> >> >>> >>    (PATCH7, PATCH8, PATCH9, PATCH14, PATCH16, PATCH17, PATCH18, PATCH19,
> >> >>> >>     PATCH20, PATCH21, PATCH22, PATCH23, and PATCH32 of
> >> >>> >>     https://lore.kernel.org/linux-arm-kernel/20221121135653.208611233@linutronix.de/)
> >> >>> >>  - Updated APLIC MSI-mode driver to use the new WIRED_TO_MSI mechanism.
> >> >>> >>  - Updated IMSIC driver to support per-device MSI domains for PCI and
> >> >>> >>    platform devices.
> >> >>> >
> >> >>> > Thanks for working on this, Anup! I'm still reviewing the patches.
> >> >>> >
> >> >>> > I'm hitting a boot hang in text patching, with this series applied on
> >> >>> > 6.8-rc2. IPI issues?
> >> >>>
> >> >>> Not text patching! One cpu spinning in smp_call_function_many_cond() and
> >> >>> the others are in cpu_relax(). Smells like IPI...
> >> >>
> >> >> I tried bootefi from U-Boot multiple times but can't reproduce the
> >> >> issue you are seeing.
> >> >
> >> > Thanks! I can reproduce without EFI, and simpler command-line:
> >> >
> >> > qemu-system-riscv64 \
> >> >   -bios /path/to/fw_dynamic.bin \
> >> >   -kernel /path/to/Image \
> >> >   -append 'earlycon console=tty0 console=ttyS0' \
> >> >   -machine virt,aia=aplic-imsic \
> >> >   -no-reboot -nodefaults -nographic \
> >> >   -smp 4 \
> >> >   -object rng-random,filename=/dev/urandom,id=rng0 \
> >> >   -device virtio-rng-device,rng=rng0 \
> >> >   -m 4G -chardev stdio,id=char0 -serial chardev:char0
> >> >
> >> > I can reproduce with your upstream riscv_aia_v12 plus the config in the
> >> > gist [1], and all latest QEMU/OpenSBI:
> >> >
> >> > QEMU: 11be70677c70 ("Merge tag 'pull-vfio-20240129' of https://github.com/legoater/qemu into staging")
> >> > OpenSBI: bb90a9ebf6d9 ("lib: sbi: Print number of debug triggers found")
> >> > Linux: d9b9d6eb987f ("MAINTAINERS: Add entry for RISC-V AIA drivers")
> >> >
> >> > Removing ",aia=aplic-imsic" from the CLI above completes the boot (i.e.
> >> > panicking about missing root mount ;-))
> >>
> >> More context; The hang is during a late initcall, where an ftrace direct
> >> (register_ftrace_direct()) modification is done.
> >>
> >> Stop machine is used to call into __ftrace_modify_call(). Then into the
> >> arch specific patch_text_nosync(), where flush_icache_range() hangs in
> >> flush_icache_all(). From "on_each_cpu(ipi_remote_fence_i, NULL, 1);" to
> >> on_each_cpu_cond_mask() "smp_call_function_many_cond(mask, func, info,
> >> scf_flags, cond_func);" which never returns from "csd_lock_wait(csd)"
> >> right before the end of the function.
> >>
> >> Any ideas? Disabling CONFIG_HID_BPF, that does the early ftrace code
> >> patching fixes the boot hang, but it does seem related to IPI...
> >>
> > Looks like flush_icache_all() does not use the IPIs (on_each_cpu()
> > and friends) correctly.
> >
> > On other hand, the flush_icache_mm() does the right thing by
> > doing local flush on the current CPU and IPI based flush on other
> > CPUs.
> >
> > Can you try the following patch ?
> >
> > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c
> > index 55a34f2020a8..a3dfbe4de832 100644
> > --- a/arch/riscv/mm/cacheflush.c
> > +++ b/arch/riscv/mm/cacheflush.c
> > @@ -19,12 +19,18 @@ static void ipi_remote_fence_i(void *info)
> >
> >  void flush_icache_all(void)
> >  {
> > +    cpumask_t others;
> > +
> >      local_flush_icache_all();
> >
> > +    cpumask_andnot(&others, cpu_online_mask, cpumask_of(smp_processor_id()));
> > +    if (cpumask_empty(&others))
> > +        return;
> > +
> >      if (IS_ENABLED(CONFIG_RISCV_SBI) && !riscv_use_ipi_for_rfence())
> > -        sbi_remote_fence_i(NULL);
> > +        sbi_remote_fence_i(&others);
> >      else
> > -        on_each_cpu(ipi_remote_fence_i, NULL, 1);
> > +        on_each_cpu_mask(&others, ipi_remote_fence_i, NULL, 1);
> >  }
> >  EXPORT_SYMBOL(flush_icache_all);
>
> Unfortunately, I see the same hang. LMK if you'd like me to try anything
> else.

I was able to reproduce this at my end but I had to use your config.

Digging further, it seems the issue is observed only when we use
in-kernel IPIs for cache flushing (instead of SBI calls) along with
some of the tracers (or debugging features) enabled. With the tracers
(or debug features) disabled we don't see any issue. In fact, the
upstream defconfig works perfectly fine with AIA drivers and
in-kernel IPIs.

It seems AIA based in-kernel IPIs are exposing some other issue
with RISC-V kernel. I will debug more to find the root cause.

Regards,
Anup