[PATCH v4 3/3] lib: sbi: domain FP/Vector context support for context switch

[Dave Patel]

On 5/13/26 08:54, Anup Patel wrote:
> On Wed, May 13, 2026 at 12:44 PM <dave.patel at riscstar.com> wrote:
>>
>> 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 hart_context`.
>> - Introduced dynamic vector struct allocation for vlenb in 'struct hart_context'
>>   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.
>> - Added runtime checks for FP and vector extensions where needed.
>>
>> 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>
>> ---
>>  include/sbi/sbi_domain.h     |  2 ++
>>  lib/sbi/sbi_domain_context.c | 28 ++++++++++++++++++++++++++++
>>  2 files changed, 30 insertions(+)
>>
>> diff --git a/include/sbi/sbi_domain.h b/include/sbi/sbi_domain.h
>> index 882b62c2..05a5d86c 100644
>> --- a/include/sbi/sbi_domain.h
>> +++ b/include/sbi/sbi_domain.h
>> @@ -16,6 +16,8 @@
>>  #include <sbi/sbi_hartmask.h>
>>  #include <sbi/sbi_domain_context.h>
>>  #include <sbi/sbi_domain_data.h>
>> +#include <sbi/sbi_vector.h>
>> +#include <sbi/sbi_fp.h>
>>
>>  struct sbi_scratch;
>>
>> diff --git a/lib/sbi/sbi_domain_context.c b/lib/sbi/sbi_domain_context.c
>> index 158f4990..5e180698 100644
>> --- a/lib/sbi/sbi_domain_context.c
>> +++ b/lib/sbi/sbi_domain_context.c
>> @@ -18,6 +18,9 @@
>>  #include <sbi/sbi_domain_context.h>
>>  #include <sbi/sbi_platform.h>
>>  #include <sbi/sbi_trap.h>
>> +#include <sbi/sbi_vector.h>
>> +#include <sbi/sbi_fp.h>
>> +
>>
>>  /** Context representation for a hart within a domain */
>>  struct hart_context {
>> @@ -55,6 +58,11 @@ struct hart_context {
>>         struct hart_context *prev_ctx;
>>         /** Is context initialized and runnable */
>>         bool initialized;
>> +
>> +       /** float context state */
>> +       struct sbi_fp_context fp_ctx;
>> +       /** vector context state */
>> +       struct sbi_vector_context *vec_ctx;
>>  };
>>
>>  static struct sbi_domain_data dcpriv;
>> @@ -143,6 +151,15 @@ static int switch_to_next_domain_context(struct hart_context *ctx,
>>         if (sbi_hart_has_extension(scratch, SBI_HART_EXT_SSQOSID))
>>                 ctx->srmcfg     = csr_swap(CSR_SRMCFG, dom_ctx->srmcfg);
>>
>> +       /* Make sure FS and VS is on before context switch */
>> +       csr_set(CSR_MSTATUS, MSTATUS_FS | MSTATUS_VS);
>> +
>> +       /* Eager context switch F and V */
>> +       sbi_fp_save(&ctx->fp_ctx);
>> +       sbi_fp_restore(&dom_ctx->fp_ctx);
>> +       sbi_vector_save(ctx->vec_ctx);
>> +       sbi_vector_restore(dom_ctx->vec_ctx);
> 
> Unconditional save/restore of FP and Vector is not going to fly
> because the generic platform firmwares are expected to work
> on multiple platforms (both with or without vector).
> 
> To address this, do FP save/restore only if underlying hart
> has F/D hart extension. Similarly, do Vector save/restore
> only if underlying hart has Vector extension.
> 
> As a separate patch, introduce SBI_HART_EXT_F,
> SBI_HART_EXT_D, and SBI_HART_EXT_V in
> enum sbi_hart_extensions and sbi_hart_ext[]. Once,
> this is done you can check for SBI_HART_EXT_F,
> SBI_HART_EXT_D, and SBI_HART_EXT_V using
> sbi_hart_has_extension().
> 

Ok will extend the enum sbi_hart_extensions and shall do check before
save/restore of the context

>> +
>>         /* Save current trap state and restore target domain's trap state */
>>         trap_ctx = sbi_trap_get_context(scratch);
>>         sbi_memcpy(&ctx->trap_ctx, trap_ctx, sizeof(*trap_ctx));
>> @@ -170,6 +187,10 @@ static int hart_context_init(u32 hartindex)
>>  {
>>         struct hart_context *ctx;
>>         struct sbi_domain *dom;
>> +       unsigned long vlenb = vector_vlenb();
>> +
>> +       /* Calculate size: base struct + 32 registers of vlenb size */
>> +       size_t vec_size = sizeof(struct sbi_vector_context) + (32 * vlenb);
>>
>>         sbi_domain_for_each(dom) {
>>                 if (!sbi_hartmask_test_hartindex(hartindex,
>> @@ -180,6 +201,13 @@ static int hart_context_init(u32 hartindex)
>>                 if (!ctx)
>>                         return SBI_ENOMEM;
>>
>> +               /* Allocate the vector context pointer */
>> +               ctx->vec_ctx = sbi_zalloc(vec_size);
>> +               if (!ctx->vec_ctx) {
>> +                       sbi_free(ctx);
>> +                       return SBI_ENOMEM;
>> +               }
>> +
>>                 /* Bind context and domain */
>>                 ctx->dom = dom;
>>                 hart_context_set(dom, hartindex, ctx);
>> --
>> 2.43.0
>>
>>
>> --
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>> opensbi at lists.infradead.org
>> http://lists.infradead.org/mailman/listinfo/opensbi
> 
> Regards,
> Anup

Hi Anup,
        Thanks, Ok understood I will extend the enum sbi_hart_extensions
and will add another patch on top of this 3rd patch to add and check the
extension.

Thanks
Dave