linux-kernel - Re: [PATCH v4 12/26] KVM: x86: Move TSC fixup logic to KVM arch resume callback

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Message-ID: <YxrTsE8iT6mTCZgg@gao-cwp>
Date:   Fri, 9 Sep 2022 13:48:32 +0800
From:   Chao Gao <chao.gao@...el.com>
To:     <isaku.yamahata@...el.com>
CC:     <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Marc Zyngier <maz@...nel.org>, Will Deacon <will@...nel.org>,
        Yuan Yao <yuan.yao@...ux.intel.com>,
        <isaku.yamahata@...il.com>, Kai Huang <kai.huang@...el.com>,
        Atish Patra <atishp@...shpatra.org>,
        Shaokun Zhang <zhangshaokun@...ilicon.com>,
        Qi Liu <liuqi115@...wei.com>,
        John Garry <john.garry@...wei.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        "Huang Ying" <ying.huang@...el.com>,
        Huacai Chen <chenhuacai@...nel.org>
Subject: Re: [PATCH v4 12/26] KVM: x86: Move TSC fixup logic to KVM arch
 resume callback

On Thu, Sep 08, 2022 at 04:25:28PM -0700, isaku.yamahata@...el.com wrote:
>From: Isaku Yamahata <isaku.yamahata@...el.com>
>
>commit 0dd6a6edb012 ("KVM: Dont mark TSC unstable due to S4 suspend") made
>use of kvm_arch_hardware_enable() callback to detect that TSC goes backward
>due to S4 suspend.  It has to check it only when resuming from S4. Not
>every time virtualization hardware ennoblement.  Move the logic to
>kvm_arch_resume() callback.

IIUC, kvm_arch_resume() is called on the first CPU waking up from suspension.
But the detection was done on every CPU. Is it a problem (i.e., we fail to
detect TSC goes backward on some CPUs)?