Re: [PATCH v2 08/10] Documentation: admin-guide: Add riscv sysctl_perf_user_access

[Alexandre Ghiti]

On 31/05/2023 17:07, Andrew Jones wrote:
> On Fri, May 12, 2023 at 10:53:19AM +0200, Alexandre Ghiti wrote:
> > riscv now uses this sysctl so document its usage for this architecture.
> >
> > Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx>
> > ---
> >   Documentation/admin-guide/sysctl/kernel.rst | 24 +++++++++++++++++----
> >   1 file changed, 20 insertions(+), 4 deletions(-)
> >
> > diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
> > index 4b7bfea28cd7..93cd518ca94b 100644
> > --- a/Documentation/admin-guide/sysctl/kernel.rst
> > +++ b/Documentation/admin-guide/sysctl/kernel.rst
> > @@ -941,16 +941,32 @@ enabled, otherwise writing to this file will return ``-EBUSY``.
> >   The default value is 8.
> >   
> >   
> > -perf_user_access (arm64 only)
> > -=================================
> > +perf_user_access (arm64 and riscv only)
> > +=======================================
> > +
> > +Controls user space access for reading perf event counters.
> >   
> > -Controls user space access for reading perf event counters. When set to 1,
> > -user space can read performance monitor counter registers directly.
> > +arm64
> > +=====
> >   
> >   The default value is 0 (access disabled).
> > +When set to 1, user space can read performance monitor counter registers
> > +directly.
> >   
> >   See Documentation/arm64/perf.rst for more information.
> >   
> > +riscv
> > +=====
> > +
> > +When set to 0, user access is disabled.
> > +
> > +When set to 1, user space can read performance monitor counter registers
> > +directly only through perf, any direct access without perf intervention will
> > +trigger an illegal instruction.
> > +
> > +The default value is 2, which enables legacy mode (user space has direct
> > +access to cycle, time and insret CSRs only). Note that this legacy value
> > +is deprecated and will be removed once all userspace applications are fixed.
> All modes can access the time CSR so I'm not sure if it should be pointed
> out here as if it's an exception. Maybe we shouldn't point it out at all
> or we should point it out for all three?


Ok I removed the reference to the time CSR for the legacy mode and 
instead added a note stating that this CSR is always accessible whatever 
the mode.

Thanks!


> Thanks,
> drew