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

[Guo Ren]

On Sat, Nov 15, 2025 at 11:05 AM Guo Ren <guoren at kernel.org> wrote:
>
> On Fri, Nov 14, 2025 at 9:55 PM Radim Krčmář <rkrcmar at ventanamicro.com> wrote:
> >
> > 2025-11-14T19:57:22+08:00, <cp0613 at linux.alibaba.com>:
> > > From: Chen Pei <cp0613 at 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 at 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,
> For multiple domains, the srmcfg(QoS ID Pool) must be managed globally
> in m-mode, or domain A would affect domain B by using its own srmcfg.
>
> Compared to switching the srmcfg, I prefer to enable SMSTATEEN0_SRMCFG
> only in one domain (the default one).
Leaving it away is more considerable.

Think about the CoVE scenario: Domain A (KVM) sets up QoS_ID, then
Domain B (TVM) uses the QoS_ID from Domain A. Thus, TVM lets regular
Linux KVM manage the QoS_ID & CBQRI.

>
> --
> Best Regards
>  Guo Ren



-- 
Best Regards
 Guo Ren