linux-kernel - Re: [PATCH] [v2] x86: xen: add missing prototypes

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Date:   Tue, 23 May 2023 19:09:06 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Arnd Bergmann <arnd@...db.de>, Arnd Bergmann <arnd@...nel.org>,
        Juergen Gross <jgross@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        Stefano Stabellini <sstabellini@...nel.org>
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>,
        Peter Zijlstra <peterz@...radead.org>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [v2] x86: xen: add missing prototypes



On 5/23/23 4:37 PM, Arnd Bergmann wrote:
> On Sat, May 20, 2023, at 00:24, Boris Ostrovsky wrote:
>> On 5/19/23 5:28 AM, Arnd Bergmann wrote:
>>
>>> diff --git a/arch/x86/xen/smp.h b/arch/x86/xen/smp.h
>>> index 22fb982ff971..81a7821dd07f 100644
>>> --- a/arch/x86/xen/smp.h
>>> +++ b/arch/x86/xen/smp.h
>>> @@ -1,7 +1,11 @@
>>>    /* SPDX-License-Identifier: GPL-2.0 */
>>>    #ifndef _XEN_SMP_H
>>>    
>>> +void asm_cpu_bringup_and_idle(void);
>>> +asmlinkage void cpu_bringup_and_idle(void);
>>
>> These can go under CONFIG_SMP
> 
> Not sure if there is much point for the second one, since
> it's only called from assembler, so the #else path is
> never seen, but I can do that for consistency if you
> like.
> 
> I generally prefer to avoid the extra #if checks
> when there is no strict need for an empty stub.

Do we need the empty stubs? Neither of these should be referenced if !SMP (or more precisely if !CONFIG_XEN_PV_SMP)

> 
> I guess you also want me to add the empty stubs for the
> other functions that only have a bit in #ifdef but not
> #else then?
> 
>>> +void xen_force_evtchn_callback(void);
>>
>> These ...
>>
>>> +pteval_t xen_pte_val(pte_t pte);
>>> +pgdval_t xen_pgd_val(pgd_t pgd);
>>> +pte_t xen_make_pte(pteval_t pte);
>>> +pgd_t xen_make_pgd(pgdval_t pgd);
>>> +pmdval_t xen_pmd_val(pmd_t pmd);
>>> +pmd_t xen_make_pmd(pmdval_t pmd);
>>> +pudval_t xen_pud_val(pud_t pud);
>>> +pud_t xen_make_pud(pudval_t pud);
>>> +p4dval_t xen_p4d_val(p4d_t p4d);
>>> +p4d_t xen_make_p4d(p4dval_t p4d);
>>> +pte_t xen_make_pte_init(pteval_t pte);
>>> +void xen_start_kernel(struct start_info *si);
>>
>>
>> ... should go under '#ifdef CONFIG_XEN_PV'
> 
> What should the stubs do here? I guess just return the
> unmodified value?


Same here -- these should only be referenced if CONFIG_XEN_PV is defined which is why I suggested moving them under ifdef.


-boris