RE: [PATCH v4 02/24] xen: consolidate cpuid library

["Penny, Zheng" <penny.zheng@xxxxxxx>]

[Public]

> -----Original Message-----
> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Tuesday, November 25, 2025 2:39 PM
> To: Penny, Zheng <penny.zheng@xxxxxxx>; Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>
> Cc: Huang, Ray <Ray.Huang@xxxxxxx>; grygorii_strashko@xxxxxxxx; Roger
> Pau Monné <roger.pau@xxxxxxxxxx>; Anthony PERARD
> <anthony.perard@xxxxxxxxxx>; Juergen Gross <jgross@xxxxxxxx>; xen-
> devel@xxxxxxxxxxxxxxxxxxxx
> Subject: Re: [PATCH v4 02/24] xen: consolidate cpuid library
>
> On 21.11.2025 11:57, Penny Zheng wrote:
> > There are some cpuid library functions only referenced in
> > XEN_DOMCTL_get{,set}_cpu_policy-case, and shall be wrapped with
> > CONFIG_MGMT_HYPERCALLS later, otherwise they will become unreachable
> > when MGMT_HYPERCALLS=n, and hence violate Misra 2.1
> > - x86_cpu_policy_clear_out_of_range_leaves
> >   - zero_leaves
> > - x86_cpuid_copy_to_buffer
> >   - copy_leaf_to_buffer
> > - x86_cpuid_copy_from_buffer
> > We seperate these functions by moving other functions to a new file
> > named cpuid-generic.c, and modify related Makefile-s to retain same 
> > behavior.
> >
> > Signed-off-by: Penny Zheng <Penny.Zheng@xxxxxxx>
> > ---
> > v3 -> v4:
> > - new commit
> > ---
> >  tools/fuzz/cpu-policy/Makefile               |   2 +-
> >  tools/fuzz/x86_instruction_emulator/Makefile |  10 +-
> >  tools/libs/guest/Makefile.common             |   2 +-
> >  tools/tests/cpu-policy/Makefile              |   2 +-
> >  tools/tests/x86_emulator/Makefile            |   2 +-
> >  xen/lib/x86/Makefile                         |   1 +
> >  xen/lib/x86/cpuid-generic.c                  | 273 +++++++++++++++++++
> >  xen/lib/x86/cpuid.c                          | 260 ------------------
> >  8 files changed, 283 insertions(+), 269 deletions(-)  create mode
> > 100644 xen/lib/x86/cpuid-generic.c
>
> Andrew - what's your take on such a split? Personally I'm not overly happy to 
> see
> related functions be scattered across two files. The separation also feels 
> pretty
> random, posing the risk that later some of the code may need to move back.
>

Right now, I could not think a better way to guard 
x86_cpuid_copy_from{,to}_buffer with MGMT_HYPERCALLS without split, any better 
suggestion? Or maybe I could add up some explanations on the file 
cpuid_generic.c head note to explain the diffs between itself and cpuid.c, 
something like:
```
The difference between cpuid.c and cpuid_generic.c is that the former contains 
library functions that has only been referenced in management hypercalls, such 
as sysctl, domctl, etc. See comment for MGMT_HYPERCALLS.
```

> Penny, I also don't think "consolidate" is what is happening here.
> Perhaps "split" would be getting closer?
>
> Jan