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

[Paolo Bonzini]

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.

Paolo