Re: [PATCH] arch/x86/entry_fred: don't set up KVM IRQs if KVM is disabled

[Borislav Petkov]

+ Arnd for

https://lore.kernel.org/r/20240216202527.2493264-1-arnd@xxxxxxxxxx

On Fri, Feb 16, 2024 at 07:31:46AM +0100, Paolo Bonzini wrote:
> On 2/16/24 03:10, Xin Li wrote:
> > On 2/15/2024 11:55 AM, Sean Christopherson wrote:
> > > +Paolo and Stephen
> > > 
> > > FYI, there's a build failure in -next due to a collision between
> > > kvm/next and
> > > tip/x86/fred.  The above makes everything happy.
> > > 
> > > On Thu, Feb 15, 2024, Max Kellermann wrote:
> > > > When KVM is disabled, the POSTED_INTR_* macros do not exist, and the
> > > > build fails.
> > > > 
> > > > Fixes: 14619d912b65 ("x86/fred: FRED entry/exit and dispatch code")
> > > > Signed-off-by: Max Kellermann <max.kellermann@xxxxxxxxx>
> > > > ---
> > > >   arch/x86/entry/entry_fred.c | 2 ++
> > > >   1 file changed, 2 insertions(+)
> > > > 
> > > > diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c
> > > > index ac120cbdaaf2..660b7f7f9a79 100644
> > > > --- a/arch/x86/entry/entry_fred.c
> > > > +++ b/arch/x86/entry/entry_fred.c
> > > > @@ -114,9 +114,11 @@ static idtentry_t
> > > > sysvec_table[NR_SYSTEM_VECTORS] __ro_after_init = {
> > > >       SYSVEC(IRQ_WORK_VECTOR,            irq_work),
> > > > +#if IS_ENABLED(CONFIG_KVM)
> > > >       SYSVEC(POSTED_INTR_VECTOR,        kvm_posted_intr_ipi),
> > > >       SYSVEC(POSTED_INTR_WAKEUP_VECTOR,    kvm_posted_intr_wakeup_ipi),
> > > >       SYSVEC(POSTED_INTR_NESTED_VECTOR,    kvm_posted_intr_nested_ipi),
> > > > +#endif
> > > >   };
> > > >   static bool fred_setup_done __initdata;
> > > > -- 
> > > > 2.39.2
> > 
> > We want to minimize #ifdeffery (which is why we didn't add any to
> > sysvec_table[]), would it be better to simply remove "#if
> > IS_ENABLED(CONFIG_KVM)" around the the POSTED_INTR_* macros from the
> > Linux-next tree?
> > 
> > BTW, kvm_posted_intr_*() are defined to NULL if !IS_ENABLED(CONFIG_KVM).
> 
> It is intentional that KVM-related things are compiled out completely
> if !IS_ENABLED(CONFIG_KVM), because then it's also not necessary to have
> 
> # define fred_sysvec_kvm_posted_intr_ipi                NULL
> # define fred_sysvec_kvm_posted_intr_wakeup_ipi         NULL
> # define fred_sysvec_kvm_posted_intr_nested_ipi         NULL
> 
> in arch/x86/include/asm/idtentry.h. The full conflict resultion is
> 
> diff --git a/arch/x86/entry/entry_fred.c b/arch/x86/entry/entry_fred.c
> index ac120cbdaaf2..660b7f7f9a79 100644
> --- a/arch/x86/entry/entry_fred.c
> +++ b/arch/x86/entry/entry_fred.c
> @@ -114,9 +114,11 @@ static idtentry_t sysvec_table[NR_SYSTEM_VECTORS] __ro_after_init = {
>      SYSVEC(IRQ_WORK_VECTOR,            irq_work),
> +#if IS_ENABLED(CONFIG_KVM)
>      SYSVEC(POSTED_INTR_VECTOR,        kvm_posted_intr_ipi),
>      SYSVEC(POSTED_INTR_WAKEUP_VECTOR,    kvm_posted_intr_wakeup_ipi),
>      SYSVEC(POSTED_INTR_NESTED_VECTOR,    kvm_posted_intr_nested_ipi),
> +#endif
>  };
>  static bool fred_setup_done __initdata;
> diff --git a/arch/x86/include/asm/idtentry.h b/arch/x86/include/asm/idtentry.h
> index 749c7411d2f1..758f6a2838a8 100644
> --- a/arch/x86/include/asm/idtentry.h
> +++ b/arch/x86/include/asm/idtentry.h
> @@ -745,10 +745,6 @@ DECLARE_IDTENTRY_SYSVEC(IRQ_WORK_VECTOR,        sysvec_irq_work);
>  DECLARE_IDTENTRY_SYSVEC(POSTED_INTR_VECTOR,        sysvec_kvm_posted_intr_ipi);
>  DECLARE_IDTENTRY_SYSVEC(POSTED_INTR_WAKEUP_VECTOR,    sysvec_kvm_posted_intr_wakeup_ipi);
>  DECLARE_IDTENTRY_SYSVEC(POSTED_INTR_NESTED_VECTOR,    sysvec_kvm_posted_intr_nested_ipi);
> -#else
> -# define fred_sysvec_kvm_posted_intr_ipi        NULL
> -# define fred_sysvec_kvm_posted_intr_wakeup_ipi        NULL
> -# define fred_sysvec_kvm_posted_intr_nested_ipi        NULL
>  #endif
>  #if IS_ENABLED(CONFIG_HYPERV)
> 
> and it seems to be a net improvement to me.  The #ifs match in
> the .h and .c files, and there are no unnecessary initializers
> in the sysvec_table.

Ok, I'll pick up Max' patch tomorrow and we must remember to tell Linus
during the merge window about this.

Thx.

-- 
Regards/Gruss,
    Boris.

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