Re: [XEN PATCH] xen: cache clearing and invalidation helpers refactoring

[Nicola Vetrini <nicola.vetrini@bugseng.com>]

On 2024-02-26 11:51, Jan Beulich wrote:
> On 23.02.2024 08:58, Nicola Vetrini wrote:
>> On 2024-02-19 16:14, Nicola Vetrini wrote:
>>> The cache clearing and invalidation helpers in x86 and Arm didn't
>>> comply with MISRA C Rule 17.7: "The value returned by a function
>>> having non-void return type shall be used". On Arm they
>>> were always returning 0, while some in x86 returned -EOPNOTSUPP
>>> and in common/grant_table the return value is saved.
>>> 
>>> As a consequence, a common helper arch_grant_cache_flush that returns
>>> an integer is introduced, so that each architecture can choose 
>>> whether
>>> to
>>> return an error value on certain conditions, and the helpers have
>>> either
>>> been changed to return void (on Arm) or deleted entirely (on x86).
>>> 
>>> Signed-off-by: Julien Grall <julien@xen.org>
>>> Signed-off-by: Nicola Vetrini <nicola.vetrini@bugseng.com>
>>> ---
>>> The original refactor idea came from Julien Grall in [1]; I edited 
>>> that
>>> proposal
>>> to fix build errors.
>>> 
>>> I did introduce a cast to void for the call to flush_area_local on 
>>> x86,
>>> because
>>> even before this patch the return value of that function wasn't 
>>> checked
>>> in all
>>> but one use in x86/smp.c, and in this context the helper (perhaps
>>> incidentally)
>>> ignored the return value of flush_area_local.
>>> 
>>> [1]
>>> https://lore.kernel.org/xen-devel/09589e8f-77b6-47f7-b5bd-cf485e4b60f1@xen.org/
>>> ---
>>>  xen/arch/arm/include/asm/page.h     | 33 
>>> ++++++++++++++++++-----------
>>>  xen/arch/x86/include/asm/flushtlb.h | 23 ++++++++++----------
>>>  xen/common/grant_table.c            |  9 +-------
>>>  3 files changed, 34 insertions(+), 31 deletions(-)
>>> 
>> 
>> I'll put this patch in the backlog at the moment: too many intricacies
>> while trying to untangle xen/flushtlb from xen/mm.h, and there are
>> easier cases that can be done faster. If someone is interested I can
>> post the partial work I've done so far, even though it doesn't
>> build on x86.
> 
> This
> https://lists.xen.org/archives/html/xen-devel/2024-02/msg01513.html
> may be of interest to you in the context here.
> 

I'll take a look, thanks.

-- 
Nicola Vetrini, BSc
Software Engineer, BUGSENG srl (https://bugseng.com)