[PATCH] lib: sbi: Refine the settings for switching to Virtual Supervisor Mode.

[Pope B.Lei]

Dear All:
     I discovered a subtle bug during the process of switching to VS
mode. The issue arises because, even though Mstatus.MPV is set, before
executing mret, one should access the VS mode registers using their
actual addresses, rather than using the pseudonyms of the S registers.

Best Regards!

Boswell Lei

On Tue, Apr 9, 2024 at 10:24 AM Pope B.Lei <popeblei at gmail.com> wrote:
>
> Although Mstatus.MPV is set, before executing mret, access to VS mode
> registers should use the actual register addresses, not the pseudonyms
> of S registers.
>
> Signed-off-by: Pope B.Lei <popeblei at gmail.com>
> ---
>  lib/sbi/sbi_hart.c | 15 +++++++++++----
>  1 file changed, 11 insertions(+), 4 deletions(-)
>
> diff --git a/lib/sbi/sbi_hart.c b/lib/sbi/sbi_hart.c
> index 3d13694..e145cdc 100644
> --- a/lib/sbi/sbi_hart.c
> +++ b/lib/sbi/sbi_hart.c
> @@ -1041,10 +1041,17 @@ sbi_hart_switch_mode(unsigned long arg0, unsigned long arg1,
>         csr_write(CSR_MEPC, next_addr);
>
>         if (next_mode == PRV_S) {
> -               csr_write(CSR_STVEC, next_addr);
> -               csr_write(CSR_SSCRATCH, 0);
> -               csr_write(CSR_SIE, 0);
> -               csr_write(CSR_SATP, 0);
> +               if (true == next_virt){
> +                   csr_write(CSR_VSTVEC, next_addr);
> +                   csr_write(CSR_VSSCRATCH, 0);
> +                   csr_write(CSR_VSIE, 0);
> +                   csr_write(CSR_VSATP, 0);
> +               } else if (false == next_virt){
> +                   csr_write(CSR_STVEC, next_addr);
> +                   csr_write(CSR_SSCRATCH, 0);
> +                   csr_write(CSR_SIE, 0);
> +                   csr_write(CSR_SATP, 0);
> +               }
>         } else if (next_mode == PRV_U) {
>                 if (misa_extension('N')) {
>                         csr_write(CSR_UTVEC, next_addr);
> --
> 2.35.2.windows.1
>