On Sun, Jul 06, 2014 at 05:24:27PM +0200, Jan Kiszka wrote: > On 2014-07-06 17:12, Gleb Natapov wrote: > > On Sat, Jul 05, 2014 at 09:47:54AM +0200, Jan Kiszka wrote: > >> From: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> > >> > >> We are able to use x2APIC mode in the absence of interrupt remapping on > >> certain hypervisors. So it if fine to disable IRQ_REMAP without having > >> to give up x2APIC support. > > FWIW I did similar thing back when I added x2apic to KVM: > > http://linux.derkeiler.com/Mailing-Lists/Kernel/2009-06/msg14579.html > > But was advised against it. > > I don't get the point from that thread. It is not architectural to use x2apic without irq remapping, so Suresh from Intel felt that it should not be allowed to create a kernel that can run on real HW and has non architectural configuration compiled in, though only when running on a VM x2apic will ever be enabled without irq remapping. I didn't argue about it to much back then. If HYPERVISOR_GUEST guaranties that resulting kernel can run only on a VM (does it?) this objection does not hold any more. > > However, this change is just formalizing a configuration that is already > being used: there is no interrupt remapping available with KVM (yet), > but we do run our guests in x2APIC mode most of the time. Interrupt > remapping code in kernels tailored as KVM guest is dead code, right now. Yes. I am just saying why things are the way they are. > > Jan > > > > >> > >> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> > >> --- > >> arch/x86/Kconfig | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > >> index a8f749e..30a9987 100644 > >> --- a/arch/x86/Kconfig > >> +++ b/arch/x86/Kconfig > >> @@ -310,7 +310,7 @@ config SMP > >> > >> config X86_X2APIC > >> bool "Support x2apic" > >> - depends on X86_LOCAL_APIC && X86_64 && IRQ_REMAP > >> + depends on X86_LOCAL_APIC && X86_64 && (IRQ_REMAP || HYPERVISOR_GUEST) > >> ---help--- > >> This enables x2apic support on CPUs that have this feature. > >> > >> > >> > > > > > > > > -- > > Gleb. > > > > -- Gleb. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
