[PATCH v3 3/3] lib: sbi: domain FP/Vector context support for context switch

[Dave Patel]

On 3/30/26 13:53, Radim Krcmar wrote:
> 2026-03-27T17:16:01+00:00, <dave.patel at riscstar.com>:
>> From: Dave Patel <dave.patel at riscstar.com>
>>
>> This patch adds proper support for per-domain floating-point (FP) and
>> vector (V) contexts in the domain context switch logic. Each domain
>> now maintains its own FP and vector state, which is saved and restored
>> during domain switches.
>>
>> Changes include:
>>
>> - Added `fp_ctx` and `vec_ctx` members to `struct sbi_domain`.
>> - Introduced `sbi_fp_domain_init/exit()` and `sbi_vector_domain_init/exit()`
>>   to allocate and free per-domain FP and vector context.
>> - Modified `sbi_domain_register()` to initialize FP/Vector context per domain.
>> - Updated `switch_to_next_domain_context()` to save/restore FP and vector
>>   contexts safely:
>>     - Ensures FS/VS fields in `mstatus` are enabled (set to Initial) only if Off.
>>     - Restores original FS/VS bits after context switch.
>>     - Adds NULL checks to handle domains without FP or Vector extensions.
>> - Updated domain context deinit to free FP and vector contexts per domain.
>> - Added runtime checks for FP and vector extensions where needed.
>> - Corrected handling of MSTATUS FS/VS bits to avoid unsafe full-bit writes.
>>
>> This improves support for multi-domain systems with FP and Vector
>> extensions, and prevents corruption of FP/Vector state during domain
>> switches.
>>
>> Signed-off-by: Dave Patel <dave.patel at riscstar.com>
>> ---
>> diff --git a/include/sbi/sbi_domain.h b/include/sbi/sbi_domain.h
>> @@ -217,6 +217,10 @@ struct sbi_domain {
>>  	bool fw_region_inited;
>>  	/** per-domain wired-IRQ courier state */
>>  	void *virq_priv;
>> +    /** per-domain float context state */
>> +	void *fp_ctx;
>> +    /** per-domain vector context state */
>> +    	void *vec_ctx;
> 
> Since the domain creation fails when F/V state cannot be allocated, why
> put the structures in sbi_domain directly?
> 
>> diff --git a/lib/sbi/sbi_domain_context.c b/lib/sbi/sbi_domain_context.c
>> @@ -143,6 +146,37 @@ static int switch_to_next_domain_context(struct hart_context *ctx,
>> +    /* Read current mstatus */
>> +    unsigned long mstatus = csr_read(CSR_MSTATUS);
>> +    unsigned long new_mstatus = mstatus;
>> +
>> +    /* Ensure FS is enabled (not Off) */
>> +    if ((mstatus & MSTATUS_FS) == 0)
>> +        new_mstatus |= MSTATUS_FS;
>> +
>> +#ifdef __riscv_v
>> +    /* Ensure VS is enabled (not Off) */
>> +    if ((mstatus & MSTATUS_VS) == 0)
>> +        new_mstatus |= MSTATUS_VS;
>> +#endif
>> +
>> +    /* Update mstatus only if needed */
>> +    if (new_mstatus != mstatus)
>> +    csr_write(CSR_MSTATUS, new_mstatus);
>> +
>> +    /* Save current domain context and restore target domain's F and V context */
>> +    sbi_fp_save(current_dom->fp_ctx);
>> +    sbi_fp_restore(target_dom->fp_ctx);
>> +#ifdef __riscv_v
>> +    sbi_vector_save(current_dom->vec_ctx);
>> +    sbi_vector_restore(target_dom->vec_ctx);
>> +#endif
>> +
>> +    /* Restore original mstatus if we modified it */
>> +    if (new_mstatus != mstatus) {
>> +        csr_write(CSR_MSTATUS, mstatus);
>> +    }
> 
> I would slightly prefer if M-mode entry always set mstatus.FS and VS to
> Off, so M-mode couldn't touch the state by mistake.
> 
> Here we'd temporarily allow M-mode to manipulate the F/V state.
> 
> Before mreting, we would restore the mstatus.FS/VS.
> 
> Thanks.

Hi Radim,
         I have accidentally sent v1 patch, Samuel H. have had similar
observation and is already taken into consideration.
I will be sending correct patch.

Thanks
Dave