Re: [PATCH v3 3/8] RISC-V: Check scalar unaligned access on all CPUs

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On 7/10/24 11:55, Evan Green wrote:
On Mon, Jun 24, 2024 at 5:51 PM Jesse Taube <jesse@xxxxxxxxxxxx> wrote:

Originally, the check_unaligned_access_emulated_all_cpus function
only checked the boot hart. This fixes the function to check all
harts.

Fixes: 71c54b3d169d ("riscv: report misaligned accesses emulation to hwprobe")
Signed-off-by: Jesse Taube <jesse@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
V1 -> V2:
  - New patch
V2 -> V3:
  - Split patch
---
  arch/riscv/kernel/traps_misaligned.c | 23 ++++++-----------------
  1 file changed, 6 insertions(+), 17 deletions(-)

diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
index b62d5a2f4541..8fadbe00dd62 100644
--- a/arch/riscv/kernel/traps_misaligned.c
+++ b/arch/riscv/kernel/traps_misaligned.c
@@ -526,31 +526,17 @@ int handle_misaligned_store(struct pt_regs *regs)
         return 0;
  }

-static bool check_unaligned_access_emulated(int cpu)
+static void check_unaligned_access_emulated(struct work_struct *unused)
  {
+       int cpu = smp_processor_id();
         long *mas_ptr = per_cpu_ptr(&misaligned_access_speed, cpu);
         unsigned long tmp_var, tmp_val;
-       bool misaligned_emu_detected;

         *mas_ptr = RISCV_HWPROBE_MISALIGNED_UNKNOWN;

         __asm__ __volatile__ (
                 "       "REG_L" %[tmp], 1(%[ptr])\n"
                 : [tmp] "=r" (tmp_val) : [ptr] "r" (&tmp_var) : "memory");
-
-       misaligned_emu_detected = (*mas_ptr == RISCV_HWPROBE_MISALIGNED_EMULATED);
-       /*
-        * If unaligned_ctl is already set, this means that we detected that all
-        * CPUS uses emulated misaligned access at boot time. If that changed
-        * when hotplugging the new cpu, this is something we don't handle.
-        */
-       if (unlikely(unaligned_ctl && !misaligned_emu_detected)) {
-               pr_crit("CPU misaligned accesses non homogeneous (expected all emulated)\n");
-               while (true)
-                       cpu_relax();
-       }

This chunk was meant to detect and refuse to run on a system where a
heterogeneous CPU is hotplugged into a previously homogenous system.
The commit message doesn't mention this change, how come you
deleted it?

Sorry for the long wait.
I do not remember why I removed this.
Your right it shouldn't be removed, I added it back.

Thanks,
Jesse Taube


-
-       return misaligned_emu_detected;
  }

  bool check_unaligned_access_emulated_all_cpus(void)
@@ -562,8 +548,11 @@ bool check_unaligned_access_emulated_all_cpus(void)
          * accesses emulated since tasks requesting such control can run on any
          * CPU.
          */
+       schedule_on_each_cpu(check_unaligned_access_emulated);
+
         for_each_online_cpu(cpu)
-               if (!check_unaligned_access_emulated(cpu))
+               if (per_cpu(misaligned_access_speed, cpu)
+                   != RISCV_HWPROBE_MISALIGNED_EMULATED)
                         return false;

         unaligned_ctl = true;
--
2.45.2





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