From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39501) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aLuA4-0004wP-4D for qemu-devel@nongnu.org; Wed, 20 Jan 2016 09:55:05 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1aLu9z-0002XA-H0 for qemu-devel@nongnu.org; Wed, 20 Jan 2016 09:55:04 -0500 Received: from mx2.parallels.com ([199.115.105.18]:55423) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1aLu9z-0002Vz-Aw for qemu-devel@nongnu.org; Wed, 20 Jan 2016 09:54:59 -0500 References: <1450949580-25759-1-git-send-email-asmetanin@virtuozzo.com> <569DEA3B.2040107@openvz.org> <569F9419.4000601@redhat.com> <569F9D61.5020203@openvz.org> <20160120145218.GH26969@rkaganb.sw.ru> From: "Denis V. Lunev" Message-ID: <569F9FBA.9040405@openvz.org> Date: Wed, 20 Jan 2016 17:54:50 +0300 MIME-Version: 1.0 In-Reply-To: <20160120145218.GH26969@rkaganb.sw.ru> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v1] kvm/x86: Hyper-V tsc page setup List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Roman Kagan , Paolo Bonzini , Andrey Smetanin , kvm@vger.kernel.org, Gleb Natapov , qemu-devel@nongnu.org On 01/20/2016 05:52 PM, Roman Kagan wrote: > On Wed, Jan 20, 2016 at 05:44:49PM +0300, Denis V. Lunev wrote: >> On 01/20/2016 05:05 PM, Paolo Bonzini wrote: >>> On 19/01/2016 08:48, Denis V. Lunev wrote: >>>>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >>>>> index 6877b4d7e..93c9e25 100644 >>>>> --- a/include/linux/kvm_host.h >>>>> +++ b/include/linux/kvm_host.h >>>>> @@ -145,6 +145,7 @@ static inline bool is_error_page(struct page *page) >>>>> #define KVM_REQ_HV_RESET 29 >>>>> #define KVM_REQ_HV_EXIT 30 >>>>> #define KVM_REQ_HV_STIMER 31 >>>>> +#define KVM_REQ_HV_TSC_PAGE 32 >>>>> #define KVM_REQ_MAX 64 >>>> ping >>> Applied with this change: >>> >>> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c >>> index d7716c6e2752..047c275717d3 100644 >>> --- a/arch/x86/kvm/hyperv.c >>> +++ b/arch/x86/kvm/hyperv.c >>> @@ -842,7 +842,7 @@ int kvm_hv_setup_tsc_page(struct kvm_vcpu *vcpu) >>> tsc_khz, tsc, tsc_scale, tsc_offset); >>> tsc_ref.tsc_sequence++; >>> - if (tsc_ref.tsc_sequence == 0) >>> + if (tsc_ref.tsc_sequence == 0xFFFFFFFF tsc_ref.tsc_sequence == 0) >>> tsc_ref.tsc_sequence = 1; >>> tsc_ref.tsc_scale = tsc_scale; >>> >>> and renumbering KVM_REQ_HV_TSC_PAGE from 32 to 31. >>> >>> Paolo >> the latter does not seem to be correct to me. >> MS spec has bug, see this thread: >> https://lkml.org/lkml/2015/11/2/655 >> and the change was Acked-by: K.Y. > What happens in the patched code is this: when the sequence counter > wraps around and hits an invalid value, skip to the next valid one. > > I think Paolo wanted to be compatible not only with the de facto > implementation in Windows Hyper-V guests, but also with the Linux driver > which followed the buggy spec and thought 0xFFFFFFFF to be invalid. > > So the change is fine (as long as there's || rather than a space there > ;) this seems reasonable, you are right :) Thank you for the explanation.