[PATCH 3/3] RISC-V: Fix IPI/RFENCE hmask on non-monotonic hartid ordering

[Atish Patra]

On Mon, Jan 31, 2022 at 5:26 AM Geert Uytterhoeven <geert at linux-m68k.org> wrote:
>
> If the boot CPU does not have the lowest hartid, "hartid - hbase" can
> become negative, leading to an incorrect hmask, causing userspace to
> crash with SEGV.  This is observed on e.g. Starlight Beta, where cpuid 1
> maps to hartid 0, and cpuid 0 maps to hartid 1.
>
> Fix this by detecting this case, and shifting the accumulated mask and
> updating hbase, if possible.
>
> Fixes: 26fb751ca37846c9 ("RISC-V: Do not use cpumask data structure for hartid bitmap")
> Signed-off-by: Geert Uytterhoeven <geert at linux-m68k.org>
> ---
>  arch/riscv/kernel/sbi.c | 57 ++++++++++++++++++++++++++++-------------
>  1 file changed, 39 insertions(+), 18 deletions(-)
>
> diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c
> index 22444cfcd56cc646..775d3322b422fe14 100644
> --- a/arch/riscv/kernel/sbi.c
> +++ b/arch/riscv/kernel/sbi.c
> @@ -250,7 +250,7 @@ static void __sbi_set_timer_v02(uint64_t stime_value)
>
>  static int __sbi_send_ipi_v02(const struct cpumask *cpu_mask)
>  {
> -       unsigned long hartid, cpuid, hmask = 0, hbase = 0;
> +       unsigned long hartid, cpuid, hmask = 0, hbase = 0, htop = 0;
>         struct sbiret ret = {0};
>         int result;
>
> @@ -259,16 +259,27 @@ static int __sbi_send_ipi_v02(const struct cpumask *cpu_mask)
>
>         for_each_cpu(cpuid, cpu_mask) {
>                 hartid = cpuid_to_hartid_map(cpuid);
> -               if (hmask && ((hbase + BITS_PER_LONG) <= hartid)) {
> -                       ret = sbi_ecall(SBI_EXT_IPI, SBI_EXT_IPI_SEND_IPI,
> -                                       hmask, hbase, 0, 0, 0, 0);
> -                       if (ret.error)
> -                               goto ecall_failed;
> -                       hmask = 0;
> -                       hbase = 0;
> +               if (hmask) {
> +                       if (hartid + BITS_PER_LONG <= htop ||
> +                           hbase + BITS_PER_LONG <= hartid) {
> +                               ret = sbi_ecall(SBI_EXT_IPI,
> +                                               SBI_EXT_IPI_SEND_IPI, hmask,
> +                                               hbase, 0, 0, 0, 0);
> +                               if (ret.error)
> +                                       goto ecall_failed;
> +                               hmask = 0;
> +                       } else if (hartid < hbase) {
> +                               /* shift the mask to fit lower hartid */
> +                               hmask <<= hbase - hartid;
> +                               hbase = hartid;
> +                       }
>                 }
> -               if (!hmask)
> +               if (!hmask) {
>                         hbase = hartid;
> +                       htop = hartid;
> +               } else if (hartid > htop) {
> +                       htop = hartid;
> +               }
>                 hmask |= BIT(hartid - hbase);
>         }
>
> @@ -345,7 +356,7 @@ static int __sbi_rfence_v02(int fid, const struct cpumask *cpu_mask,
>                             unsigned long start, unsigned long size,
>                             unsigned long arg4, unsigned long arg5)
>  {
> -       unsigned long hartid, cpuid, hmask = 0, hbase = 0;
> +       unsigned long hartid, cpuid, hmask = 0, hbase = 0, htop = 0;
>         int result;
>
>         if (!cpu_mask || cpumask_empty(cpu_mask))
> @@ -353,16 +364,26 @@ static int __sbi_rfence_v02(int fid, const struct cpumask *cpu_mask,
>
>         for_each_cpu(cpuid, cpu_mask) {
>                 hartid = cpuid_to_hartid_map(cpuid);
> -               if (hmask && ((hbase + BITS_PER_LONG) <= hartid)) {
> -                       result = __sbi_rfence_v02_call(fid, hmask, hbase,
> -                                                      start, size, arg4, arg5);
> -                       if (result)
> -                               return result;
> -                       hmask = 0;
> -                       hbase = 0;
> +               if (hmask) {
> +                       if (hartid + BITS_PER_LONG <= htop ||
> +                           hbase + BITS_PER_LONG <= hartid) {
> +                               result = __sbi_rfence_v02_call(fid, hmask,
> +                                               hbase, start, size, arg4, arg5);
> +                               if (result)
> +                                       return result;
> +                               hmask = 0;
> +                       } else if (hartid < hbase) {
> +                               /* shift the mask to fit lower hartid */
> +                               hmask <<= hbase - hartid;
> +                               hbase = hartid;
> +                       }
>                 }
> -               if (!hmask)
> +               if (!hmask) {
>                         hbase = hartid;
> +                       htop = hartid;
> +               } else if (hartid > htop) {
> +                       htop = hartid;
> +               }
>                 hmask |= BIT(hartid - hbase);
>         }
>
> --
> 2.25.1
>
>
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Reviewed-by: Atish Patra <atishp at rivosinc.com>
Tested-by: Atish Patra <atishp at rivosinc.com>

-- 
Regards,
Atish