linux-kernel - Re: [PATCH v6 8/8] kvm: vmx: virtualize split lock detection

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Date:   Thu, 26 Mar 2020 23:09:21 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        hpa@...or.com, Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH v6 8/8] kvm: vmx: virtualize split lock detection

On 3/26/2020 10:55 PM, Thomas Gleixner wrote:
> Xiaoyao Li <xiaoyao.li@...el.com> writes:
>> On 3/26/2020 7:10 PM, Thomas Gleixner wrote:
>> If the host has it disabled, !split_lock_detect_on() is true, it skips
>> following check due to ||
>>
>> if (!boot_cpu_has(X86_FEATURE_SPLIT_LOCK)) {
>> 	inject #AC back to guest
and 	return 1;

> 
> That'd be a regular #AC, right?

Yes.

>> } else {
>> 	if (guest_alignment_check_enabled() || guest_sld_on())
>> 		inject #AC back to guest
and 		return 1;

> Here is clearly an else path missing.

the else path is fall through.

i.e. calling handle_user_split_lock().

If cannot handle, it falls through to report #AC to user space (QEMU)

>> }
> 

If there is no problem with the above. So what's the problem of the 
original?