Re: [PATCH v3 05/22] x86/xstate: drop xstate_offsets[] and xstate_sizes[]

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 22/04/2021 15:45, Jan Beulich wrote:
> They're redundant with respective fields from the raw CPUID policy; no
> need to keep two copies of the same data.

So before I read this patch of yours, I had a separate cleanup patch
turning the two arrays into static const.

> This also breaks
> recalculate_xstate()'s dependency on xstate_init(),

It doesn't, because you've retained the reference to xstate_align, which
is calculated in xstate_init().  I've posted "[PATCH 4/5] x86/cpuid:
Simplify recalculate_xstate()" which goes rather further.

xstate_align, and xstate_xfd as you've got later in the series, don't
need to be variables.  They're constants, just like the offset/size
information, because they're all a description of the XSAVE ISA
instruction behaviour.

We never turn on states we don't understand, which means we don't
actually need to refer to any component subleaf, other than to cross-check.

I'm still on the fence as to whether it is better to compile in the
constants, or to just use the raw policy.  Absolutely nothing good will
come of the constants changing, and one of my backup plans for dealing
with the size of cpuid_policy if it becomes a problem was to not store
these leaves, and generate them dynamically on request.


> allowing host CPUID
> policy calculation to be moved together with that of the raw one (which
> a subsequent change will require anyway).

While breaking up the host/raw calculations from the rest, we really
need to group the MSR policy calculations with their CPUID counterparts.

~Andrew