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SubjectRe: [v5 PATCH] RISC-V: Fix unsupported isa string info.
Date
On Tue, 2019-08-20 at 00:59 -0700, Atish Patra wrote:
> On Sun, 2019-08-18 at 11:16 -0700, hch@infradead.org wrote:
> > On Fri, Aug 16, 2019 at 07:21:52PM +0000, Atish Patra wrote:
> > > > > + if (isa[0] != '\0') {
> > > > > + /* Add remainging isa strings */
> > > > > + for (e = isa; *e != '\0'; ++e) {
> > > > > +#if !defined(CONFIG_VIRTUALIZATION)
> > > > > + if (e[0] != 'h')
> > > > > +#endif
> > > > > + seq_write(f, e, 1);
> > > > > + }
> > > > > + }
> > > >
> > > > This one I don't get. Why do we want to check
> > > > CONFIG_VIRTUALIZATION?
> > > >
> > >
> > > If CONFIG_VIRTUALIZATION is not enabled, it shouldn't print that
> > > hypervisor extension "h" in isa extensions.
> >
> > CONFIG_VIRTUALIZATION doesn't change anything in the kernels
> > capabilities, it just enables other config options.
>
> Yes. But it must be enabled if virtualization is supported in kernel.
> The idea was to let userspace know that if virtualization can be used
> or not.
>
>
> > But more
> > importantly the 'h' extension is only relevant for S-mode software
> > anyway.
> >
>
> Do you think we should just print all the extensions available in isa
> string as it is ?
>
> > > This is just an information to the userspace that some of the
> > > mandatory
> > > ISA extensions ("mafdcsu") are not supported in kernel which may
> > > lead
> > > to undesirable results.
> >
> > I think we need to sit down decide what the purpose of
> > /proc/cpuinfo
> > is. IIRC on other architectures is just prints what the hardware
> > supports, not what you can actually make use of. How else would
> > you
> > find out that you'd need to enable more kernel options to fully
> > utilize the hardware?
> >
> > Also printing this warning to the kernel log when someone reads the
> > procfs file is very strange.
>
> Agreed. May be something like this ?
>
> Let's say f/d is enabled in kernel but cpu doesn't support it.
> "unsupported isa" will only appear if there are any unsupported isa.
>
> processor : 3
> hart : 4
> isa : rv64imac
> unsupported isa : fd
> mmu : sv39
> uarch : sifive,u54-mc
>
> May be I am just trying over optimize one corner case :) :).
> /proc/cpuinfo should just print all the isa string. That's it.
>

Ping ?

> Regards,
> Atish

--
Regards,
Atish
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