Re: [PATCH v5] lib: sbi: Enable Ssqosid Ext using mstateen0

["Radim Krčmář" <rkrcmar@ventanamicro.com>]

2025-11-14T19:57:22+08:00, <cp0613@linux.alibaba.com>:
> From: Chen Pei <cp0613@linux.alibaba.com>
>
> The QoS Identifiers extension (Ssqosid) introduces the srmcfg register,
> which configures a hart with two identifiers: a Resource Control ID
> (RCID) and a Monitoring Counter ID (MCID). These identifiers accompany
> each request issued by the hart to shared resource controllers.
>
> If extension Smstateen is implemented together with Ssqosid, then
> Ssqosid also requires the SRMCFG bit in mstateen0 to be implemented. If
> mstateen0.SRMCFG is 0, attempts to access srmcfg in privilege modes less
> privileged than M-mode raise an illegal-instruction exception. If
> mstateen0.SRMCFG is 1 or if extension Smstateen is not implemented,
> attempts to access srmcfg when V=1 raise a virtual-instruction exception.
>
> This extension can be found in the RISC-V Instruction Set Manual:
> https://github.com/riscv/riscv-isa-manual
>
> Changes in v5:
>  - Remove SBI_HART_EXT_SSQOSID dependency SBI_HART_PRIV_VER_1_12
>
> Changes in v4:
>  - Remove extraneous parentheses around SMSTATEEN0_SRMCFG
>
> Changes in v3:
>  - Check SBI_HART_EXT_SSQOSID when swapping SRMCFG
>
> Changes in v2:
>  - Remove trap-n-detect
>  - Context switch CSR_SRMCFG
>
> Signed-off-by: Chen Pei <cp0613@linux.alibaba.com>
> ---

It's possible that S-mode control over srmcfg might leak very little
information across architectural isolation boundaries, but I don't know
enough about CBQRI to mount any practical attack (it might not exist),
so the current handling seems acceptable,

Reviewed-by: Radim Krčmář <rkrcmar@ventanamicro.com>

Thanks.

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