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

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Message-ID: <877dz7x84b.fsf@nanos.tec.linutronix.de>
Date:   Thu, 26 Mar 2020 19:51:16 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Xiaoyao Li <xiaoyao.li@...el.com>, 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

Xiaoyao Li <xiaoyao.li@...el.com> writes:
> 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?

Probably my inability to decipher the convoluted condition.

Thanks,

        tglx