Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757621Ab0LBNzF (ORCPT ); Thu, 2 Dec 2010 08:55:05 -0500 Received: from smtp.ctxuk.citrix.com ([62.200.22.115]:43834 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757565Ab0LBNzE (ORCPT ); Thu, 2 Dec 2010 08:55:04 -0500 X-IronPort-AV: E=Sophos;i="4.59,288,1288569600"; d="scan'208";a="3154671" Date: Thu, 2 Dec 2010 13:54:55 +0000 From: Stefano Stabellini X-X-Sender: sstabellini@kaball-desktop To: Sheng Yang CC: Jeremy Fitzhardinge , Keir Fraser , xen-devel , "linux-kernel@vger.kernel.org" , Stefano Stabellini Subject: Re: [PATCH] xen: HVM X2APIC support In-Reply-To: <201012021433.46976.sheng@linux.intel.com> Message-ID: References: <1291258990-16080-1-git-send-email-sheng@linux.intel.com> <4CF73C80.4000101@goop.org> <201012021433.46976.sheng@linux.intel.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3869 Lines: 113 On Thu, 2 Dec 2010, Sheng Yang wrote: > On Thursday 02 December 2010 14:28:16 Jeremy Fitzhardinge wrote: > > On 12/01/2010 07:03 PM, Sheng Yang wrote: > > > This patch is similiar to Gleb Natapov's patch for KVM, which enable the > > > hypervisor to emulate x2apic feature for the guest. By this way, the > > > emulation of lapic would be simpler with x2apic interface(MSR), and > > > faster. > > > > We have a set of patches to directly use event channels from within hvm > > domains, completely bypassing the apic altogether. Do we need this as > > well? > > This is for other HVMs. And the pvhvm still have limitation like it can't use > MSI/MSI-X assigned device. That is not true: upstream Linux kernels can remap MSI/MSI-X into pirqs, if it doesn't work is a bug :) If you are interested give a look at arch/x86/pci/xen.c:xen_hvm_setup_msi_irqs. > > > > > > Signed-off-by: Sheng Yang > > > --- > > > > > > arch/x86/include/asm/xen/hypervisor.h | 33 > > > +++++++++++++++++++++++++++++++++ arch/x86/kernel/apic/apic.c > > > | 4 +++- > > > arch/x86/xen/enlighten.c | 19 ------------------- > > > 3 files changed, 36 insertions(+), 20 deletions(-) > > > > > > diff --git a/arch/x86/include/asm/xen/hypervisor.h > > > b/arch/x86/include/asm/xen/hypervisor.h index 396ff4c..e862874 100644 > > > --- a/arch/x86/include/asm/xen/hypervisor.h > > > +++ b/arch/x86/include/asm/xen/hypervisor.h > > > @@ -37,4 +37,37 @@ > > > > > > extern struct shared_info *HYPERVISOR_shared_info; > > > extern struct start_info *xen_start_info; > > > > > > +#include > > > + > > > +static inline uint32_t xen_cpuid_base(void) > > > +{ > > > + uint32_t base, eax, ebx, ecx, edx; > > > + char signature[13]; > > > + > > > + for (base = 0x40000000; base < 0x40010000; base += 0x100) { > > > + cpuid(base, &eax, &ebx, &ecx, &edx); > > > + *(uint32_t *)(signature + 0) = ebx; > > > + *(uint32_t *)(signature + 4) = ecx; > > > + *(uint32_t *)(signature + 8) = edx; > > > + signature[12] = 0; > > > + > > > + if (!strcmp("XenVMMXenVMM", signature) && ((eax - base) >= 2)) > > > + return base; > > > + } > > > + > > > + return 0; > > > +} > > > + > > > +#ifdef CONFIG_XEN > > > +static inline bool xen_para_available(void) > > > +{ > > > + return 0; > > > +} > > > +#else > > > +static inline bool xen_para_available(void) > > > +{ > > > + return (xen_cpuid_base() != 0); > > > +} > > > +#endif > > > > So this returns true if you're running a kernel without CONFIG_XEN under > > Xen? Does that assume that all versions of Xen implement x2apic > > emulation? Why wouldn't we also want this for CONFIG_XEN kernels? > > Because only the ones that implement the feature would expose x2apic CPUID. > > For CONFIG_XEN(pv or pvhvm), they both use evtchn, so no need for x2apic. In that case you need to check for CONFIG_XEN_PVHVM and the presence of xen_feature(XENFEAT_hvm_pirqs) because only in this case a PV on HVM guests are able to remap both GSIs and MSIs into evtchns. So I would do something like this: #ifdef CONFIG_XEN_PVHVM static inline bool xen_para_available(void) { if (xen_cpuid_base() != 0 && xen_feature(XENFEAT_hvm_pirqs)) return 0; else return 1; } #else static inline bool xen_para_available(void) { return (xen_cpuid_base() != 0); } #endif This is assuming that enabling x2apic doesn't prevent Linux from receiving evtchns either using the callback vector mechanism or the legacy platform-pci interrupt. Finally when running as dom0 would this feature create problems in the presence of a real x2apic? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/