Re: [PATCH] hw/intc: sifive_plic: Fix multi-socket plic configuraiton

[Alistair Francis <alistair23@gmail.com>]

On Sat, Jul 23, 2022 at 7:22 PM Atish Patra <atishp@rivosinc.com> wrote:
>
> Since commit 40244040a7ac, multi-socket configuration with plic is
> broken as the hartid for second socket is calculated incorrectly.
> The hartid stored in addr_config already includes the offset
> for the base hartid for that socket. Adding it again would lead
> to segfault while creating the plic device for the virt machine.
> qdev_connect_gpio_out was also invoked with incorrect number of gpio
> lines.
>
> Fixes: 40244040a7ac (hw/intc: sifive_plic: Avoid overflowing the addr_config buffer)
>
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
>  hw/intc/sifive_plic.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/hw/intc/sifive_plic.c b/hw/intc/sifive_plic.c
> index 56d60e9ac935..fdac028a521f 100644
> --- a/hw/intc/sifive_plic.c
> +++ b/hw/intc/sifive_plic.c
> @@ -454,10 +454,10 @@ DeviceState *sifive_plic_create(hwaddr addr, char *hart_config,
>
>      for (i = 0; i < plic->num_addrs; i++) {
>          int cpu_num = plic->addr_config[i].hartid;
> -        CPUState *cpu = qemu_get_cpu(hartid_base + cpu_num);
> +        CPUState *cpu = qemu_get_cpu(cpu_num);
>
>          if (plic->addr_config[i].mode == PLICMode_M) {
> -            qdev_connect_gpio_out(dev, num_harts + cpu_num,
> +            qdev_connect_gpio_out(dev, cpu_num,

Argh!

I was trying to get this ready to go into 7.1. I have been working on
updating my tests to catch this failure in the future as well.

While testing this change I noticed that it breaks the noMMU test case.

I think the correct fix is actually this (on top of your patch):

diff --git a/hw/intc/sifive_plic.c b/hw/intc/sifive_plic.c
index fdac028a52..af4ae3630e 100644
--- a/hw/intc/sifive_plic.c
+++ b/hw/intc/sifive_plic.c
@@ -457,7 +457,7 @@ DeviceState *sifive_plic_create(hwaddr addr, char
*hart_config,
        CPUState *cpu = qemu_get_cpu(cpu_num);

        if (plic->addr_config[i].mode == PLICMode_M) {
-            qdev_connect_gpio_out(dev, cpu_num,
+            qdev_connect_gpio_out(dev, num_harts - plic->hartid_base + cpu_num,
                                  qdev_get_gpio_in(DEVICE(cpu), IRQ_M_EXT));
        }
        if (plic->addr_config[i].mode == PLICMode_S) {

The idea is that we need to increment the second argument to
qdev_connect_gpio_out() for the PLICMode_M compared to the PLICMode_S
case.

This ensures that we do that correctly without breaking anything.

How does that look to you?

Alistair

>                                    qdev_get_gpio_in(DEVICE(cpu), IRQ_M_EXT));
>          }
>          if (plic->addr_config[i].mode == PLICMode_S) {
> --
> 2.25.1
>
>