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Date:   Tue, 23 Aug 2022 15:50:09 +0800
From:   Chao Gao <chao.gao@intel.com>
To:     <isaku.yamahata@intel.com>
CC:     <kvm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <isaku.yamahata@gmail.com>, Paolo Bonzini <pbonzini@redhat.com>,
        "Sean Christopherson" <seanjc@google.com>,
        Kai Huang <kai.huang@intel.com>,
        "Will Deacon" <will@kernel.org>
Subject: Re: [RFC PATCH 12/18] KVM: Do processor compatibility check on cpu
 online and resume
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 <60f9ec74499c673c474e9d909c2f3176bc6711c3.1660974106.git.isaku.yamahata@intel.com>
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On Fri, Aug 19, 2022 at 11:00:18PM -0700, isaku.yamahata@intel.com wrote:
>From: Isaku Yamahata <isaku.yamahata@intel.com>
>
>So far the processor compatibility check is not done for newly added CPU.
>It should be done.
>
>Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
>---
> virt/kvm/kvm_arch.c | 20 +++++++++++++++-----
> 1 file changed, 15 insertions(+), 5 deletions(-)
>
>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.

>+	return __hardware_enable();
> }
> 
> __weak int kvm_arch_offline_cpu(unsigned int cpu, int usage_count)
>@@ -126,6 +132,10 @@ __weak int kvm_arch_suspend(int usage_count)
> 
> __weak void kvm_arch_resume(int usage_count)
> {
>-	if (usage_count)
>-		(void)__hardware_enable();
>+	if (!usage_count)
>+		return;
>+
>+	if (kvm_arch_check_processor_compat())
>+		return; /* FIXME: disable KVM */

Ditto.

>+	(void)__hardware_enable();
> }
>-- 
>2.25.1
>