From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752153AbdAMPcD (ORCPT ); Fri, 13 Jan 2017 10:32:03 -0500 Received: from mx1.redhat.com ([209.132.183.28]:44505 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752005AbdAMPcB (ORCPT ); Fri, 13 Jan 2017 10:32:01 -0500 Date: Fri, 13 Jan 2017 16:31:58 +0100 From: Radim Krcmar To: Marcelo Tosatti Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Paolo Bonzini , Richard Cochran , Miroslav Lichvar Subject: Re: [patch 2/3] KVM: x86: add KVM_HC_CLOCK_OFFSET hypercall Message-ID: <20170113153157.GB25835@potion> References: <20170113120131.086634482@redhat.com> <20170113120319.692007194@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170113120319.692007194@redhat.com> X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Fri, 13 Jan 2017 15:32:01 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2017-01-13 10:01-0200, Marcelo Tosatti: > Add a hypercall to retrieve the host realtime clock > and the TSC value used to calculate that clock read. > > Used to implement clock synchronization between > host and guest. > > Signed-off-by: Marcelo Tosatti > > --- > Documentation/virtual/kvm/hypercalls.txt | 30 ++++++++++++++++++++++ > arch/x86/include/uapi/asm/kvm_para.h | 9 ++++++ > arch/x86/kvm/x86.c | 41 +++++++++++++++++++++++++++++++ > include/uapi/linux/kvm_para.h | 3 ++ > 4 files changed, 83 insertions(+) > > Index: kvm-ptpdriver/arch/x86/include/uapi/asm/kvm_para.h > =================================================================== > --- kvm-ptpdriver.orig/arch/x86/include/uapi/asm/kvm_para.h 2017-01-13 09:03:33.823305270 -0200 > +++ kvm-ptpdriver/arch/x86/include/uapi/asm/kvm_para.h 2017-01-13 09:07:54.633699270 -0200 > @@ -50,6 +50,15 @@ > __u32 pad[11]; > }; > > +#define KVM_CLOCK_OFFSET_WALLCLOCK 0 > +struct kvm_clock_offset { > + __s64 sec; > + __s64 nsec; > + __u64 tsc; > + __u32 flags; > + __u32 pad[1]; > +}; > + > #define KVM_STEAL_ALIGNMENT_BITS 5 > #define KVM_STEAL_VALID_BITS ((-1ULL << (KVM_STEAL_ALIGNMENT_BITS + 1))) > #define KVM_STEAL_RESERVED_MASK (((1 << KVM_STEAL_ALIGNMENT_BITS) - 1 ) << 1) > Index: kvm-ptpdriver/Documentation/virtual/kvm/hypercalls.txt > =================================================================== > --- kvm-ptpdriver.orig/Documentation/virtual/kvm/hypercalls.txt 2017-01-13 09:03:33.823305270 -0200 > +++ kvm-ptpdriver/Documentation/virtual/kvm/hypercalls.txt 2017-01-13 09:15:32.971389949 -0200 > @@ -81,3 +81,33 @@ > same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall, > specifying APIC ID (a1) of the vcpu to be woken up. An additional argument (a0) > is used in the hypercall for future use. > + > + > +6. KVM_HC_CLOCK_OFFSET > +------------------------ > +Architecture: x86 > +Status: active > +Purpose: Hypercall used to synchronize host and guest clocks. > +Usage: > + > +a0: guest physical address where host copies > +"struct kvm_clock_offset" structure. > + > +a1: clock_type, ATM only KVM_CLOCK_OFFSET_WALLCLOCK (0) > +is supported (hosts CLOCK_REALTIME clock). > + > + struct kvm_clock_offset { > + __s64 sec; > + __s64 nsec; Why is nsec: 1) signed -- it is a remainder after division by NSEC_PER_SEC 2) bigger than 32 bit -- NSEC_PER_SEC < 2^32 ? > + __u64 tsc; > + __u32 flags; > + __u32 pad; > + }; > + > + Where: > + * sec: seconds from clock_type clock. > + * nsec: nanoseconds from clock_type clock. The important part of an offset is the starting point -- I assume it is the the usual one, but documentation better be explicit. > + * tsc: TSC value used to calculate sec/nsec pair This hypercall could in theory work even when computing the offset with a different clocksource on the host and the estimating TSC at that time. > + (this hypercall only works when host uses TSC clocksource). Describe that error as a return value. > + * flags: flags, unused at the moment. unused = 0. > + > Index: kvm-ptpdriver/arch/x86/kvm/x86.c > =================================================================== > --- kvm-ptpdriver.orig/arch/x86/kvm/x86.c 2017-01-13 09:04:46.581415259 -0200 > +++ kvm-ptpdriver/arch/x86/kvm/x86.c 2017-01-13 09:08:51.557785166 -0200 > @@ -6121,6 +6121,44 @@ > } > EXPORT_SYMBOL_GPL(kvm_emulate_halt); > > +static int kvm_pv_clock_offset(struct kvm_vcpu *vcpu, gpa_t paddr, > + unsigned long clock_type) > +{ > + struct kvm_clock_offset *clock_offset; > + struct timespec ts; > + cycle_t cycle; > + int ret; > + > + if (clock_type != KVM_CLOCK_OFFSET_WALLCLOCK) > + return -KVM_EOPNOTSUPP; > + > + if (pvclock_gtod_data.clock.vclock_mode != VCLOCK_TSC) > + return -KVM_EOPNOTSUPP; > + > + clock_offset = kzalloc(sizeof(struct kvm_clock_offset), GFP_KERNEL); Can't clock_offset be on the stack? > + if (clock_offset == NULL) > + return -KVM_ENOMEM; > + > + if (kvm_get_walltime_and_clockread(&ts, &cycle) == false) { > + kfree(clock_offset); > + return -KVM_EOPNOTSUPP; > + } > + > + clock_offset->sec = ts.tv_sec; > + clock_offset->nsec = ts.tv_nsec; > + clock_offset->tsc = kvm_read_l1_tsc(vcpu, cycle); > + clock_offset->flags = 0; > + > + ret = 0; > + if (kvm_write_guest(vcpu->kvm, paddr, clock_offset, > + sizeof(struct kvm_clock_offset))) > + ret = -KVM_EFAULT; > + > + kfree(clock_offset); > + > + return ret; > +} > + > /* > * kvm_pv_kick_cpu_op: Kick a vcpu. > * > @@ -6185,6 +6223,9 @@ > kvm_pv_kick_cpu_op(vcpu->kvm, a0, a1); > ret = 0; > break; > + case KVM_HC_CLOCK_OFFSET: > + ret = kvm_pv_clock_offset(vcpu, a0, a1); > + break; > default: > ret = -KVM_ENOSYS; > break; > Index: kvm-ptpdriver/include/uapi/linux/kvm_para.h > =================================================================== > --- kvm-ptpdriver.orig/include/uapi/linux/kvm_para.h 2017-01-13 09:03:33.823305270 -0200 > +++ kvm-ptpdriver/include/uapi/linux/kvm_para.h 2017-01-13 09:07:54.636699274 -0200 > @@ -14,6 +14,8 @@ > #define KVM_EFAULT EFAULT > #define KVM_E2BIG E2BIG > #define KVM_EPERM EPERM > +#define KVM_EOPNOTSUPP EOPNOTSUPP > +#define KVM_ENOMEM ENOMEM > > #define KVM_HC_VAPIC_POLL_IRQ 1 > #define KVM_HC_MMU_OP 2 > @@ -23,6 +25,7 @@ > #define KVM_HC_MIPS_GET_CLOCK_FREQ 6 > #define KVM_HC_MIPS_EXIT_VM 7 > #define KVM_HC_MIPS_CONSOLE_OUTPUT 8 > +#define KVM_HC_CLOCK_OFFSET 9 > > /* > * hypercalls use architecture specific > >