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([2001:b07:6468:f312:b8fe:679e:87eb:c059]) by smtp.gmail.com with ESMTPSA id k8sm3102469wrl.3.2020.01.23.05.54.50 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 23 Jan 2020 05:54:50 -0800 (PST) Subject: Re: [PATCH 2/2] KVM: x86: use raw clock values consistently To: Vitaly Kuznetsov Cc: mtosatti@redhat.com, stable@vger.kernel.org, linux-kernel@vger.kernel.org, kvm@vger.kernel.org References: <1579702953-24184-1-git-send-email-pbonzini@redhat.com> <1579702953-24184-3-git-send-email-pbonzini@redhat.com> <87r1zqqode.fsf@vitty.brq.redhat.com> From: Paolo Bonzini Message-ID: Date: Thu, 23 Jan 2020 14:54:47 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <87r1zqqode.fsf@vitty.brq.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 23/01/20 14:43, Vitaly Kuznetsov wrote: >> + >> +static s64 get_kvmclock_base_ns(void) >> +{ >> + /* Count up from boot time, but with the frequency of the raw clock. */ >> + return ktime_to_ns(ktime_add(ktime_get_raw(), pvclock_gtod_data.offs_boot)); >> +} >> +#else >> +static s64 get_kvmclock_base_ns(void) >> +{ >> + /* Master clock not used, so we can just use CLOCK_BOOTTIME. */ >> + return ktime_get_boottime_ns(); >> +} >> #endif > But we could've still used the RAW+offs_boot version, right? And this is > just to basically preserve the existing behavior on !x86. Yes, there's no reason to restrict the pvclock_gtod notifier to x86_64. But this is stable material so I kept it easy. >> >> - getboottime64(&boot); >> + wall_nsec = ktime_get_real_ns() - get_kvmclock_ns(kvm); > > There are not that many hosts with more than 50 years uptime and likely > none running Linux with live kernel patching support so I bet noone will > ever see this overflowing, however, as wall_nsec is u64 and we're > dealing with kvmclock here I'd suggest to add a WARN_ON(). You're off by a factor of 10, 2^64 nanoseconds are about 584 years (584*365*10^9*86400). :) Paolo