On Fri, Aug 25, 2023 at 04:11:38PM -0700, Evan Green wrote: > In /proc/cpuinfo, most of the information we show for each processor is > specific to that hart: marchid, mvendorid, mimpid, processor, hart, > compatible, and the mmu size. But the ISA string gets filtered through a > lowest common denominator mask, so that if one CPU is missing an ISA > extension, no CPUs will show it. > > Now that we track the ISA extensions for each hart, let's report ISA > extension info accurately per-hart in /proc/cpuinfo. We cannot change > the "isa:" line, as usermode may be relying on that line to show only > the common set of extensions supported across all harts. Add a new "hart > isa" line instead, which reports the true set of extensions for that > hart. > > Signed-off-by: Evan Green <evan@xxxxxxxxxxxx> > Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx> > Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx> Can you drop this if you repost? > +"isa" vs "hart isa" lines in /proc/cpuinfo > +------------------------------------------ > + > +The "isa" line in /proc/cpuinfo describes the lowest common denominator of > +RISC-V ISA extensions recognized by the kernel and implemented on all harts. The > +"hart isa" line, in contrast, describes the set of extensions recognized by the > +kernel on the particular hart being described, even if those extensions may not > +be present on all harts in the system. > In both cases, the presence of a feature > +in these lines guarantees only that the hardware has the described capability. > +Additional kernel support or policy control changes may be required before a > +feature is fully usable by userspace programs. I do not think that "in both cases" matches the expectations of userspace for the existing line. It's too late at night for me to think properly, but I think our existing implementation does work like you have documented for FD/V. I think I previously mentioned that it could misreport things for vector during the review of the vector series but forgot about it until now.
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