linux-kernel - Re: [RFC PATCH 12/18] KVM: Do processor compatibility check on cpu online and resume

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Message-ID: <20220823080831.GE2147148@ls.amr.corp.intel.com>
Date:   Tue, 23 Aug 2022 01:08:31 -0700
From:   Isaku Yamahata <isaku.yamahata@...il.com>
To:     Chao Gao <chao.gao@...el.com>
Cc:     isaku.yamahata@...el.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kai Huang <kai.huang@...el.com>, Will Deacon <will@...nel.org>
Subject: Re: [RFC PATCH 12/18] KVM: Do processor compatibility check on cpu
 online and resume

On Tue, Aug 23, 2022 at 03:50:09PM +0800,
Chao Gao <chao.gao@...el.com> wrote:

> >diff --git a/virt/kvm/kvm_arch.c b/virt/kvm/kvm_arch.c
> >index 2ed8de0591c9..20971f43df95 100644
> >--- a/virt/kvm/kvm_arch.c
> >+++ b/virt/kvm/kvm_arch.c
> >@@ -99,9 +99,15 @@ __weak int kvm_arch_del_vm(int usage_count)
> > 
> > __weak int kvm_arch_online_cpu(unsigned int cpu, int usage_count)
> > {
> >-	if (usage_count)
> >-		return __hardware_enable();
> >-	return 0;
> >+	int r;
> >+
> >+	if (!usage_count)
> >+		return 0;
> >+
> >+	r = kvm_arch_check_processor_compat();
> >+	if (r)
> >+		return r;
> 
> I think kvm_arch_check_processor_compat() should be called even when
> usage_count is 0. Otherwise, compatibility checks may be missing on some
> CPUs if no VM is running when those CPUs becomes online.

Oh, right. Compatibility check should be done unconditionally.
-- 
Isaku Yamahata <isaku.yamahata@...il.com>