On 02/02/2023 11:08 am, Luca Fancellu wrote: > Recent changes added in struct xen_sysctl_physinfo a new flag for > arch_capabilities to understand when the platform is SVE capable, > another field having the maximum SVE vector length in bits was > added as well, so update the tools to handle these new fields. > > Signed-off-by: Luca Fancellu <luca.fance...@arm.com> > --- > Changes from RFC: > - new patch > --- > This patch is mostly dependent on the decisions we make in the previous, > anyway > I touched some part of the toolstack where my knowledge is limited (ocaml) so > I might need a feedback for something I may have done wrong.
There's a lot of ifdefary here which is going to make the code impossible to maintain, especially in python and xl where you're playing games with the position of the comma. But taking a step back. First, split this series into two (even if it's first half / second half of a single series that you email out). How to report the presence of a capability is different from how to configure the capability for a guest, and should be done separately. But even still. SVE is a single bit feature. physinfo is the wrong place to report it, and I dont see any need for it to be in the domain construction hypercall. Both are critically space-limited structures. ARM needs to gain something similar to x86's cpu policy architecture, both in terms of sysctls reporting system capabilities, and domctls to get/set domain configuration. Looking at your cover letter, SVE (in terms of what it means for Xen) looks quite similar to x86's AMX and Arch-LBR insofar as it's a large amount of new register state that we don't want to allocate for guests not making use of it. On x86, what we're planning to do (It's not done yet, because I keep on getting preempted with security work) is to require the toolstack to make a set_cpu_policy hypercall between createdomain and maxcpus to configure the size of XSAVE state, after which vcpu_create() in the hypervisor has the info it needs to construct backing state correctly. I know I'm telling you to do a lot of work, but bodging SVE in like this isn't ok. Someone *is* going to have to do proper feature configuration on ARM, and I guarantee you that it will be less effort to do it properly now, than to retrofit it in the future. x86 has been a nightmare to untangle 15 years of bad interface design in a way that doesn't regress behaviour. ~Andrew
