[RFC PATCH 2/2] lib: sbi: Preserve supervisor CTR records across domain switches

[Anup Patel]

On Fri, Oct 23, 2026 at 9:08 AM whensun
<theodoruswensanfebruanto025 at gmail.com> wrote:
>
> From: Theodorus Wensan Februanto <theodoruswensanfebruanto025 at gmail.com>
>
> Save supervisor CTR control, depth, status, and logical record
> entries when Ssctr and Sscsrind are available. This experimental
> implementation freezes recording before saving and restores
> status before logical records.
>
> IMSIC and other indirect CSR state remain outside this change.
>
> Link: https://github.com/riscv-software-src/opensbi/issues/433
> Signed-off-by: Theodorus Wensan Februanto <theodoruswensanfebruanto025 at gmail.com>
> ---
>  lib/sbi/sbi_domain_context.c | 95 ++++++++++++++++++++++++++++++++++++
>  1 file changed, 95 insertions(+)
>
> diff --git a/lib/sbi/sbi_domain_context.c b/lib/sbi/sbi_domain_context.c
> index 14927ff5..af180409 100644
> --- a/lib/sbi/sbi_domain_context.c
> +++ b/lib/sbi/sbi_domain_context.c
> @@ -21,6 +21,24 @@
>  #include <sbi/sbi_vector.h>
>  #include <sbi/sbi_fp.h>
>
> +#define HART_CTR_MAX_ENTRIES 256
> +#define HART_CTR_FIRST_SELECTOR 0x200
> +#define HART_CTR_FROZEN (1UL << 31)
> +
> +struct hart_ctr_entry {
> +       unsigned long source;
> +       unsigned long target;
> +       unsigned long data;
> +};
> +
> +struct hart_ctr_context {
> +       unsigned long ctl;
> +       unsigned long depth;
> +       unsigned long status;
> +       unsigned long vsctl;
> +       struct hart_ctr_entry entries[HART_CTR_MAX_ENTRIES];
> +};
> +
>  /** Context representation for a hart within a domain */
>  struct hart_context {
>         /** Trap-related states such as GPRs, mepc, and mstatus */
> @@ -77,6 +95,8 @@ struct hart_context {
>         unsigned long siselect;
>         /** AIA supervisor interrupt priority register bank */
>         unsigned long siprio[16];
> +       /** Supervisor control transfer records */
> +       struct hart_ctr_context *ctr_ctx;
>
>         /** Float context state */
>         struct sbi_fp_context fp_ctx;
> @@ -142,6 +162,59 @@ static void hart_aia_iprio_restore(const struct hart_context *ctx)
>         }
>  }
>
> +#if __riscv_xlen == 64
> +static unsigned int hart_ctr_entry_count(unsigned long depth)
> +{
> +       unsigned int encoding = depth & 7;
> +
> +       if (encoding > 4)
> +               return 0;
> +       return 16U << encoding;
> +}
> +
> +static void hart_ctr_save(struct hart_ctr_context *ctx)
> +{
> +       unsigned int i, count;
> +
> +       ctx->status = csr_read_set(CSR_SCTRSTATUS, HART_CTR_FROZEN);
> +       ctx->ctl = csr_read(CSR_SCTRCTL);
> +       ctx->depth = csr_read(CSR_SCTRDEPTH);
> +       if (misa_extension('H'))
> +               ctx->vsctl = csr_read(CSR_VSCTRCTL);
> +
> +       count = hart_ctr_entry_count(ctx->depth);
> +       for (i = 0; i < count; i++) {
> +               csr_write(CSR_SISELECT, HART_CTR_FIRST_SELECTOR + i);
> +               ctx->entries[i].source = csr_read(CSR_SIREG);
> +               ctx->entries[i].target = csr_read(CSR_SIREG2);
> +               ctx->entries[i].data = csr_read(CSR_SIREG3);
> +       }
> +}
> +
> +static void hart_ctr_restore(const struct hart_ctr_context *ctx)
> +{
> +       unsigned int i, count;
> +
> +       csr_write(CSR_SCTRCTL, 0);
> +       csr_write(CSR_SCTRDEPTH, ctx->depth);
> +       __asm__ __volatile__(".4byte 0x10400073" ::: "memory");
> +       csr_write(CSR_SCTRSTATUS, ctx->status | HART_CTR_FROZEN);
> +
> +       count = hart_ctr_entry_count(ctx->depth);
> +       for (i = 0; i < count; i++) {
> +               csr_write(CSR_SISELECT, HART_CTR_FIRST_SELECTOR + i);
> +               csr_write(CSR_SIREG2, ctx->entries[i].target);
> +               csr_write(CSR_SIREG3, ctx->entries[i].data);
> +               csr_write(CSR_SIREG, ctx->entries[i].source);
> +       }
> +
> +       if (misa_extension('H'))
> +               csr_write(CSR_VSCTRCTL, ctx->vsctl);
> +       csr_write(CSR_SCTRCTL, ctx->ctl);
> +       csr_write(CSR_SCTRSTATUS, ctx->status);
> +}
> +#endif
> +
>  /**
>   * Switches the HART context from the current domain to the target domain.
>   * This includes changing domain assignments and reconfiguring PMP, as well
> @@ -239,6 +312,13 @@ static int switch_to_next_domain_context(struct hart_context *ctx,
>                 hart_aia_iprio_restore(dom_ctx);
>                 csr_write(CSR_SISELECT, dom_ctx->siselect);
>         }
> +#if __riscv_xlen == 64
> +       if (ctx->ctr_ctx && dom_ctx->ctr_ctx) {
> +               hart_ctr_save(ctx->ctr_ctx);
> +               hart_ctr_restore(dom_ctx->ctr_ctx);
> +               csr_write(CSR_SISELECT, dom_ctx->siselect);
> +       }
> +#endif
>
>         /* Eager context switch for float */
>         if (sbi_hart_has_extension(scratch, SBI_HART_EXT_F) ||
> @@ -302,6 +382,20 @@ static int hart_context_init(u32 hartindex)
>
>                 ctx->stimecmp = ~0ULL;
>
> +#if __riscv_xlen == 64
> +               if (sbi_hart_has_extension(sbi_scratch_thishart_ptr(),
> +                                          SBI_HART_EXT_SSCTR) &&
> +                   sbi_hart_has_extension(sbi_scratch_thishart_ptr(),
> +                                          SBI_HART_EXT_SSCSRIND)) {
> +                       ctx->ctr_ctx = sbi_zalloc(sizeof(*ctx->ctr_ctx));
> +                       if (!ctx->ctr_ctx) {
> +                               sbi_free(ctx);
> +                               return SBI_ENOMEM;
> +                       }
> +                       ctx->ctr_ctx->depth = csr_read(CSR_SCTRDEPTH);
> +               }

Detect and save CTR depth / number_of_enteries in struct hart_features.
Also, move this detection logic in sbi_hart.c

> +#endif
> +
>                 if (sbi_hart_has_extension(sbi_scratch_thishart_ptr(),
>                                            SBI_HART_EXT_V)) {
>                         vec_size = sbi_vector_context_size();
> @@ -309,6 +403,7 @@ static int hart_context_init(u32 hartindex)
>                         /* Allocate the vector context pointer */
>                         ctx->vec_ctx = sbi_zalloc(vec_size);
>                         if (!ctx->vec_ctx) {
> +                               sbi_free(ctx->ctr_ctx);
>                                 sbi_free(ctx);
>                                 return SBI_ENOMEM;
>                         }
> --
> 2.43.0
>
>
> --
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Regards,
Anup