Hi, > On 26 Jan 2021, at 09:22, Jan Beulich <jbeul...@suse.com> wrote: > > On 25.01.2021 22:27, Stefano Stabellini wrote: >> A recent thread [1] has exposed a couple of issues with our current way >> of handling EXPERT. >> >> 1) It is not obvious that "Configure standard Xen features (expert >> users)" is actually the famous EXPERT we keep talking about on xen-devel >> >> 2) It is not obvious when we need to enable EXPERT to get a specific >> feature >> >> In particular if you want to enable ACPI support so that you can boot >> Xen on an ACPI platform, you have to enable EXPERT first. But searching >> through the kconfig menu it is really not clear (type '/' and "ACPI"): >> nothing in the description tells you that you need to enable EXPERT to >> get the option. >> >> So this patch makes things easier by doing two things: >> >> - introduce a new kconfig option UNSUPPORTED which is clearly to enable >> UNSUPPORTED features as defined by SUPPORT.md >> >> - change EXPERT options to UNSUPPORTED where it makes sense: keep >> depending on EXPERT for features made for experts >> >> - tag unsupported features by adding (UNSUPPORTED) to the one-line >> description >> >> - clarify the EXPERT one-line description >> >> [1] https://marc.info/?l=xen-devel&m=160333101228981 >> >> Signed-off-by: Stefano Stabellini <stefano.stabell...@xilinx.com> Reviewed-by: Bertrand Marquis <bertrand.marq...@arm.com>
Answering to Jan... > > Non-Arm bits > Reviewed-by: Jan Beulich <jbeul...@suse.com> > However, I have questions on the Arm ones (sorry for not noticing > earlier, as I assume it was this way before already): > >> @@ -77,7 +77,7 @@ config SBSA_VUART_CONSOLE >> SBSA Generic UART implements a subset of ARM PL011 UART. >> >> config ARM_SSBD >> - bool "Speculative Store Bypass Disable" if EXPERT >> + bool "Speculative Store Bypass Disable (UNSUPPORTED)" if UNSUPPORTED >> depends on HAS_ALTERNATIVE >> default y >> help >> @@ -87,7 +87,7 @@ config ARM_SSBD >> If unsure, say Y. >> >> config HARDEN_BRANCH_PREDICTOR >> - bool "Harden the branch predictor against aliasing attacks" if EXPERT >> + bool "Harden the branch predictor against aliasing attacks >> (UNSUPPORTED)" if UNSUPPORTED >> default y >> help >> Speculation attacks against some high-performance processors rely on > > Both of these default to y and have their _prompt_ > conditional upon EXPERT. Which means only an expert can turn them > _off_. Which doesn't make it look like these are unsupported? Or > if anything, turning them off is unsupported? ...You could see that as EXPERT/UNSUPPORTED options can only be “modified” from their default value if EXPERT/UNSUPPORTED is activated. So I find the current solution ok. If this is a problem we could also change those options to be default to _off_ by renaming them to config DISABLE_xxxx Cheers Bertrand > > Jan
