From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH] x86: Make x2APIC support depend on interrupt remapping or guest support Date: Sun, 06 Jul 2014 17:24:27 +0200 Message-ID: <53B96A2B.4040909@web.de> References: <53B7ADAA.9030101@web.de> <20140706151242.GN18167@minantech.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="bfuJHuw70tFtSQuRbJBQu9K9xb0IaHQov" Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , x86 , Linux Kernel Mailing List , kvm To: Gleb Natapov Return-path: In-Reply-To: <20140706151242.GN18167@minantech.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --bfuJHuw70tFtSQuRbJBQu9K9xb0IaHQov Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable 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 >> >> We are able to use x2APIC mode in the absence of interrupt remapping o= n >> 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. 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. Jan >=20 >> >> Signed-off-by: Jan Kiszka >> --- >> 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 >> =20 >> 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_GUES= T) >> ---help--- >> This enables x2apic support on CPUs that have this feature. >> =20 >> >> >=20 >=20 >=20 > -- > Gleb. >=20 --bfuJHuw70tFtSQuRbJBQu9K9xb0IaHQov Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.19 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iEYEARECAAYFAlO5ai0ACgkQitSsb3rl5xRvaACfSR8fN4+9TTpBNpSEjUcUAlwB ceEAnjykP+L1tJ3RWVNgYQ+OFd/6HiJX =WLTj -----END PGP SIGNATURE----- --bfuJHuw70tFtSQuRbJBQu9K9xb0IaHQov--