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

["Björn Töpel" <bjorn@kernel.org>]

Anup Patel <apatel@ventanamicro.com> writes:

> On Tue, Jan 30, 2024 at 11:19 PM Björn Töpel <bjorn@kernel.org> wrote:
>>
>> Anup Patel <apatel@ventanamicro.com> writes:
>>
>> > On Tue, Jan 30, 2024 at 8:18 PM Björn Töpel <bjorn@kernel.org> wrote:
>> >>
>> >> Björn Töpel <bjorn@kernel.org> writes:
>> >>
>> >> > Anup Patel <apatel@ventanamicro.com> writes:
>> >> >
>> >> >> On Tue, Jan 30, 2024 at 1:22 PM Björn Töpel <bjorn@kernel.org> wrote:
>> >> >>>
>> >> >>> Björn Töpel <bjorn@kernel.org> writes:
>> >> >>>
>> >> >>> > Anup Patel <apatel@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.

Same here. I only see the issue for *one* scenario. Other than that
scenario, AIA is working fine! We're doing ftrace text patching, and I
wonder if this is the issue. RISC-V (unfortunately) still rely on
stop_machine() text patching (which will change!).

Again, the hang is in stop_machine() context, where interrupts should
very much be disabled, right? So, triggering an IPI will be impossible.

Dumping mstatus in QEMU:
  | mstatus  0000000a000000a0
  | mstatus  0000000a000000a0
  | mstatus  0000000a000000a0
  | mstatus  0000000a000000a0

Indeed sstatus.SIE is 0.

Seems like the bug is that text patching is trying to issue an IPI:
  | [<ffffffff801145d4>] smp_call_function_many_cond+0x81e/0x8ba
  | [<ffffffff80114716>] on_each_cpu_cond_mask+0x3e/0xde
  | [<ffffffff80013968>] flush_icache_all+0x98/0xc4
  | [<ffffffff80009c26>] patch_text_nosync+0x7c/0x146
  | [<ffffffff80ef9116>] __ftrace_modify_call.constprop.0+0xca/0x120
  | [<ffffffff80ef918c>] ftrace_update_ftrace_func+0x20/0x40
  | [<ffffffff80efb8ac>] ftrace_modify_all_code+0x5a/0x1d8
  | [<ffffffff80efba50>] __ftrace_modify_code+0x26/0x42
  | [<ffffffff80131734>] multi_cpu_stop+0x14e/0x1d8
  | [<ffffffff8013107a>] cpu_stopper_thread+0x9e/0x182
  | [<ffffffff80077a04>] smpboot_thread_fn+0xf8/0x1d2
  | [<ffffffff800718fc>] kthread+0xe8/0x108
  | [<ffffffff80f1cde6>] ret_from_fork+0xe/0x20


Björn

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