Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755636Ab0LCGqE (ORCPT ); Fri, 3 Dec 2010 01:46:04 -0500 Received: from mga09.intel.com ([134.134.136.24]:22841 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752189Ab0LCGqD (ORCPT ); Fri, 3 Dec 2010 01:46:03 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.59,292,1288594800"; d="scan'208";a="580152266" From: Sheng Yang Organization: Intel Opensource Technology Center To: Stefano Stabellini Subject: Re: [PATCH] xen: HVM X2APIC support Date: Fri, 3 Dec 2010 14:48:04 +0800 User-Agent: KMail/1.13.5 (Linux/2.6.35-22-generic; KDE/4.5.1; x86_64; ; ) Cc: Jeremy Fitzhardinge , Keir Fraser , "xen-devel" , "linux-kernel@vger.kernel.org" References: <1291258990-16080-1-git-send-email-sheng@linux.intel.com> <201012021433.46976.sheng@linux.intel.com> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Message-Id: <201012031448.04382.sheng@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4639 Lines: 134 On Thursday 02 December 2010 21:54:55 Stefano Stabellini wrote: > 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. That's great! > > > > > 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; I suppose only HVM guest without XENFEAT_hvm_pirqs may need this. But does this code covered PV guest as well? We don't need cover them. > } > #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. I suppose only legacy platform-pci would need this, because it would use lapic. Callback vector method would use evtchn so this won't be enabled. > Finally when running as dom0 would this feature create problems in the > presence of a real x2apic? I don't think this can be enabled on dom0. This one target on HVM domain, maybe also PVHVM domain without XENFEAT_hvm_pirqs, but not the domains using evtchn. -- regards Yang, Sheng -- 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/