Re: [PATCH v3 02/17] riscv: sbi: add FWFT extension interface

On Mon, Mar 10, 2025 at 04:12:09PM +0100, Clément Léger wrote:

This SBI extensions enables supervisor mode to control feature that are under M-mode control (For instance, Svadu menvcfg ADUE bit, Ssdbltrp DTE, etc).

Signed-off-by: Clément Léger cleger@rivosinc.com

arch/riscv/include/asm/sbi.h | 5 ++ arch/riscv/kernel/sbi.c | 97 ++++++++++++++++++++++++++++++++++++ 2 files changed, 102 insertions(+)

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h index bb077d0c912f..fc87c609c11a 100644 --- a/arch/riscv/include/asm/sbi.h +++ b/arch/riscv/include/asm/sbi.h @@ -503,6 +503,11 @@ int sbi_remote_hfence_vvma_asid(const struct cpumask *cpu_mask, unsigned long asid); long sbi_probe_extension(int ext); +int sbi_fwft_all_cpus_set(u32 feature, unsigned long value, unsigned long flags,

• 	  bool revert_on_failure);
  

+int sbi_fwft_get(u32 feature, unsigned long *value); +int sbi_fwft_set(u32 feature, unsigned long value, unsigned long flags);

/* Check if current SBI specification version is 0.1 or not */ static inline int sbi_spec_is_0_1(void) { diff --git a/arch/riscv/kernel/sbi.c b/arch/riscv/kernel/sbi.c index 1989b8cade1b..256910db1307 100644 --- a/arch/riscv/kernel/sbi.c +++ b/arch/riscv/kernel/sbi.c @@ -299,6 +299,103 @@ static int __sbi_rfence_v02(int fid, const struct cpumask *cpu_mask, return 0; } +int sbi_fwft_get(u32 feature, unsigned long *value) +{

• return -EOPNOTSUPP;

+}

+/**

• • sbi_fwft_set() - Set a feature on all online cpus

copy+paste of description from sbi_fwft_all_cpus_set(). This function only sets the feature on the calling hart.

• • @feature: The feature to be set
• • @value: The feature value to be set
• • @flags: FWFT feature set flags
• • Return: 0 on success, appropriate linux error code otherwise.
• */

+int sbi_fwft_set(u32 feature, unsigned long value, unsigned long flags) +{

• return -EOPNOTSUPP;

+}

+struct fwft_set_req {

• u32 feature;
• unsigned long value;
• unsigned long flags;
• cpumask_t mask;

+};

+static void cpu_sbi_fwft_set(void *arg) +{

• struct fwft_set_req *req = arg;
• if (sbi_fwft_set(req->feature, req->value, req->flags))

• cpumask_clear_cpu(smp_processor_id(), &req->mask);
  

+}

+static int sbi_fwft_feature_local_set(u32 feature, unsigned long value,

• 		      unsigned long flags,
  

• 		      bool revert_on_fail)
  

+{

• int ret;
• unsigned long prev_value;
• cpumask_t tmp;
• struct fwft_set_req req = {

• .feature = feature,
  

• .value = value,
  

• .flags = flags,
  

• };
• cpumask_copy(&req.mask, cpu_online_mask);
• /* We can not revert if features are locked */
• if (revert_on_fail && flags & SBI_FWFT_SET_FLAG_LOCK)

Should use () around the flags &. I thought checkpatch complained about that?

• return -EINVAL;
  

• /* Reset value is the same for all cpus, read it once. */

How do we know we're reading the reset value? sbi_fwft_all_cpus_set() may be called multiple times on the same feature. And harts may have had sbi_fwft_set() called on them independently. I think we should drop the whole prev_value optimization.

• ret = sbi_fwft_get(feature, &prev_value);
• if (ret)

• return ret;
  

• /* Feature might already be set to the value we want */
• if (prev_value == value)

• return 0;
  

• on_each_cpu_mask(&req.mask, cpu_sbi_fwft_set, &req, 1);
• if (cpumask_equal(&req.mask, cpu_online_mask))

• return 0;
  

• pr_err("Failed to set feature %x for all online cpus, reverting\n",

•       feature);
  

nit: I'd let the above line stick out. We have 100 chars.

• req.value = prev_value;
• cpumask_copy(&tmp, &req.mask);
• on_each_cpu_mask(&req.mask, cpu_sbi_fwft_set, &req, 1);
• if (cpumask_equal(&req.mask, &tmp))

• return 0;
  

I'm not sure we want the revert_on_fail support either. What happens when the revert fails and we return -EINVAL below? Also returning zero when revert succeeds means the caller won't know if we successfully set what we wanted or just successfully reverted.

• return -EINVAL;

+}

+/**

• • sbi_fwft_all_cpus_set() - Set a feature on all online cpus
• • @feature: The feature to be set
• • @value: The feature value to be set
• • @flags: FWFT feature set flags
• • @revert_on_fail: true if feature value should be restored to it's orignal

its original

• •     value on failure.
    

Line 'value' up under 'true'

• • Return: 0 on success, appropriate linux error code otherwise.
• */

+int sbi_fwft_all_cpus_set(u32 feature, unsigned long value, unsigned long flags,

• 	  bool revert_on_fail)
  

+{

• if (feature & SBI_FWFT_GLOBAL_FEATURE_BIT)

• return sbi_fwft_set(feature, value, flags);
  

• return sbi_fwft_feature_local_set(feature, value, flags,

• 			  revert_on_fail);
  

+}

/**

• sbi_set_timer() - Program the timer for next timer event.
• @stime_value: The value after which next timer event should fire.

-- 2.47.2

Thanks, drew