[PATCH] ext-sse: Handle landing pads SSTATUS.SPELP bit

[Clément Léger]

Wrong mailing list, please discard this one.

Thanks,

Clément

On 20/01/2025 10:27, Clément Léger wrote:
> When landing pads are enabled, we need to actually save and restore
> the interrupted state using SSTATUS.SPELP content. In order to match the
> Zicfilp specification, disable ELP by clearing MSTATUS.SPELP before
> entering the S-mode SSE event handler like it is done for a trap.
> 
> Signed-off-by: Clément Léger <cleger at rivosinc.com>
> ---
> 
> Note: I modified the bit ordering to keep sstatus SP* bit together but we might
> keep the existing ordering as well depending on feedback.
> 
>  src/ext-sse.adoc | 28 +++++++++++++++++++---------
>  1 file changed, 19 insertions(+), 9 deletions(-)
> 
> diff --git a/src/ext-sse.adoc b/src/ext-sse.adoc
> index c85ff14..d685ddb 100644
> --- a/src/ext-sse.adoc
> +++ b/src/ext-sse.adoc
> @@ -240,11 +240,14 @@ event attributes.
>    +
>    `bit[1:1]`: interrupted `sstatus.SPIE` CSR bit value +
>    +
> -  `bit[2:2]`: interrupted `hstatus.SPV` CSR bit value +
> +  `bit[2:2]`: interrupted `sstatus.SPELP` CSR bit value if `Zicfilp` extension
> +  is available to supervisor mode +
>    +
> -  `bit[3:3]`: interrupted `hstatus.SPVP` CSR bit value +
> +  `bit[3:3]`: interrupted `hstatus.SPV` CSR bit value +
>    +
> -  `bit[XLEN-1:4]`: Reserved for future use and should be zero +
> +  `bit[4:4]`: interrupted `hstatus.SPVP` CSR bit value +
> +  +
> +  `bit[XLEN-1:5]`: Reserved for future use and should be zero +
>  
>  | INTERRUPTED_A6
>  | 0x00000008
> @@ -281,12 +284,14 @@ following:
>    .. Set `INTERRUPTED_FLAGS` event attribute as follows:
>       ... `INTERRUPTED_FLAGS[0:0]` = interrupted `sstatus.SPP` CSR bit value
>       ... `INTERRUPTED_FLAGS[1:1]` = interrupted `sstatus.SPIE` CSR bit value
> +     ... if `Zicfilp` is available to supervisor mode:
> +     ....  `INTERRUPTED_FLAGS[2:2]` = interrupted `sstatus.SPELP` CSR bit value
>       ... if H-extension is available to supervisor mode:
> -     ....  Set `INTERRUPTED_FLAGS[2:2]` = interrupted `hstatus.SPV` CSR bit value
> -     ....  Set `INTERRUPTED_FLAGS[3:3]` = interrupted `hstatus.SPVP` CSR bit value
> +     ....  Set `INTERRUPTED_FLAGS[3:3]` = interrupted `hstatus.SPV` CSR bit value
> +     ....  Set `INTERRUPTED_FLAGS[4:4]` = interrupted `hstatus.SPVP` CSR bit value
>       ... else
> -     ....  Set `INTERRUPTED_FLAGS[3:2]` = zero
> -     ... Set `INTERRUPTED_FLAGS[XLEN-1:4]` = zero
> +     ....  Set `INTERRUPTED_FLAGS[4:3]` = zero
> +     ... Set `INTERRUPTED_FLAGS[XLEN-1:5]` = zero
>    .. Set `INTERRUPTED_SEPC` event attribute = interrupted `sepc` CSR
>    .. Set `INTERRUPTED_A6` event attribute = interrupted `A6` GPR value
>    .. Set `INTERRUPTED_A7` event attribute = interrupted `A7` GPR value
> @@ -297,10 +302,13 @@ following:
>    .. Set `sstatus.SPP` CSR bit = interrupted privilege mode
>    .. Set `sstatus.SPIE` CSR bit = `sstatus.SIE` CSR bit value
>    .. Set `sstatus.SIE` CSR bit = zero
> +  .. if `Zicfilp` is available to supervisor mode:
> +     ... Set `sstatus.SPELP` = interrupted landing pad state
>    .. if H-extension is available to supervisor mode:
>       ... Set `hstatus.SPV` CSR bit = interrupted virtualization state
>       ... if `hstatus.SPV` CSR bit == 1:
>         .... Set `hstatus.SPVP` CSR bit = `sstatus.SPP` CSR bit value
> +  .. Set landing pad state = NO_LP_EXPECTED
>    .. Set virtualization state = OFF
>    .. Set privilege mode = S-mode
>    .. Set program counter = `ENTRY_PC` event attribute value
> @@ -316,9 +324,11 @@ resume the interrupted state for a completed event:
>  . Set privilege mode = `sstatus.SPP` CSR bit value
>  . if H-extension is available to supervisor mode:
>    .. Set virtualization state = `hstatus.SPV` CSR bit value
> -  .. Set `hstatus.SPV` CSR bit = `INTERRUPTED_FLAGS[2:2]` event attribute value
> -  .. Set `hstatus.SPVP` CSR bit = `INTERRUPTED_FLAGS[3:3]` event attribute value
> +  .. Set `hstatus.SPV` CSR bit = `INTERRUPTED_FLAGS[3:3]` event attribute value
> +  .. Set `hstatus.SPVP` CSR bit = `INTERRUPTED_FLAGS[4:4]` event attribute value
>  . Set `sstatus.SIE` CSR bit = `sstatus.SPIE` CSR bit
> +. if `Zicfilp` is available to supervisor mode:
> +  .. Set `sstatus.SPELP` CSR bit = `INTERRUPTED_FLAGS[2:2]` event attribute value
>  . Set `sstatus.SPIE` CSR bit = `INTERRUPTED_FLAGS[1:1]` event attribute value
>  . Set `sstatus.SPP` CSR bit = `INTERRUPTED_FLAGS[0:0]` event attribute value
>  . Set `A7` GPR = `INTERRUPTED_A7` event attribute value