linux-kernel - Re: [PATCH] KVM: apic: avoid calculating pending eoi from an uninitialized val

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Date:   Fri, 21 Feb 2020 01:36:31 +0000
From:   linmiaohe <linmiaohe@...wei.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "wanpengli@...cent.com" <wanpengli@...cent.com>,
        "jmattson@...gle.com" <jmattson@...gle.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>
Subject: Re: [PATCH] KVM: apic: avoid calculating pending eoi from an
 uninitialized val

Sean Christopherson <sean.j.christopherson@...el.com> wrote:
>On Thu, Feb 20, 2020 at 05:33:17PM +0100, Vitaly Kuznetsov wrote:
>> linmiaohe <linmiaohe@...wei.com> writes:
>> 
>
>Rather than initialize @val, I'd prefer to explicitly handle the error, similar to pv_eoi_clr_pending() and pv_eoi_set_pending(), e.g.
>
>	u8 val;
>
>	if (pv_eoi_get_user(vcpu, &val) < 0) {
>		printk(KERN_WARNING "Can't read EOI MSR value: 0x%llx\n",
>			   (unsigned long long)vcpu->arch.pv_eoi.msr_val);
>		return false;
>	}
>	return val & 0x1;

Looks good. Handle the error explicitly can help remind us @val is unusable.
Will do. Thanks.

>> >  	if (pv_eoi_get_user(vcpu, &val) < 0)
>> >  		printk(KERN_WARNING "Can't read EOI MSR value: 0x%llx\n",
>> >  			   (unsigned long long)vcpu->arch.pv_eoi.msr_val);
>> 
>> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> 
>> But why compilers don't complain?
>
>Clang might?
>