From mboxrd@z Thu Jan 1 00:00:00 1970 From: Marcelo Tosatti Subject: Re: [PATCH 2/2] Revert "KVM: x86: zero kvmclock_offset when vcpu0 initializes kvmclock system MSR" Date: Tue, 22 Sep 2015 17:23:47 -0300 Message-ID: <20150922202345.GA29417@amt.cnet> References: <1442591670-5216-1-git-send-email-rkrcmar@redhat.com> <1442591670-5216-3-git-send-email-rkrcmar@redhat.com> <20150922190133.GB23748@amt.cnet> <5601B191.4040809@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Cc: Radim =?utf-8?B?S3LEjW3DocWZ?= , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Luiz Capitulino To: Paolo Bonzini Return-path: Content-Disposition: inline In-Reply-To: <5601B191.4040809@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On Tue, Sep 22, 2015 at 09:52:49PM +0200, Paolo Bonzini wrote: >=20 >=20 > On 22/09/2015 21:01, Marcelo Tosatti wrote: > > On Fri, Sep 18, 2015 at 05:54:30PM +0200, Radim Kr=C4=8Dm=C3=A1=C5=99= wrote: > >> Shifting pvclock_vcpu_time_info.system_time on write to KVM system= time > >> MSR is a change of ABI. Probably only 2.6.16 based SLES 10 breaks= due > >> to its custom enhancements to kvmclock, but KVM never declared the= MSR > >> only for one-shot initialization. (Doc says that only one write i= s > >> needed.) > >> > >> This reverts commit b7e60c5aedd2b63f16ef06fde4f81ca032211bc5. > >> And adds a note to the definition of PVCLOCK_COUNTS_FROM_ZERO. > >> > >> Signed-off-by: Radim Kr=C4=8Dm=C3=A1=C5=99 > >> --- > >> arch/x86/include/asm/pvclock-abi.h | 1 + > >> arch/x86/kvm/x86.c | 4 ---- > >> 2 files changed, 1 insertion(+), 4 deletions(-) > >> > >> diff --git a/arch/x86/include/asm/pvclock-abi.h b/arch/x86/include= /asm/pvclock-abi.h > >> index 655e07a48f6c..67f08230103a 100644 > >> --- a/arch/x86/include/asm/pvclock-abi.h > >> +++ b/arch/x86/include/asm/pvclock-abi.h > >> @@ -41,6 +41,7 @@ struct pvclock_wall_clock { > >> =20 > >> #define PVCLOCK_TSC_STABLE_BIT (1 << 0) > >> #define PVCLOCK_GUEST_STOPPED (1 << 1) > >> +/* PVCLOCK_COUNTS_FROM_ZERO broke ABI and can't be used anymore. = */ > >> #define PVCLOCK_COUNTS_FROM_ZERO (1 << 2) > >> #endif /* __ASSEMBLY__ */ > >> #endif /* _ASM_X86_PVCLOCK_ABI_H */ > >> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > >> index 18d59b584dee..34d33f4757d2 100644 > >> --- a/arch/x86/kvm/x86.c > >> +++ b/arch/x86/kvm/x86.c > >> @@ -1707,8 +1707,6 @@ static int kvm_guest_time_update(struct kvm_= vcpu *v) > >> vcpu->pvclock_set_guest_stopped_request =3D false; > >> } > >> =20 > >> - pvclock_flags |=3D PVCLOCK_COUNTS_FROM_ZERO; > >> - > >> /* If the host uses TSC clocksource, then it is stable */ > >> if (use_master_clock) > >> pvclock_flags |=3D PVCLOCK_TSC_STABLE_BIT; > >> @@ -2006,8 +2004,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu= , struct msr_data *msr_info) > >> &vcpu->requests); > >> =20 > >> ka->boot_vcpu_runs_old_kvmclock =3D tmp; > >> - > >> - ka->kvmclock_offset =3D -get_kernel_ns(); > >> } > >> =20 > >> vcpu->arch.time =3D data; > >> --=20 > >> 2.5.2 > >=20 > > ACK >=20 > So I suppose you changed your mind :) but can you explain the reasoni= ng? >=20 > Paolo The patch is correct. Overflow (issue raised) is only an issue=20 without PVCLOCK_TSC_STABLE_BIT.