linux-kernel - Re: [PATCH] x86/Hyper-V: Support for free page reporting

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Date:   Wed, 20 May 2020 09:05:26 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Sunil Muthuswamy <sunilmut@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <liuwe@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>
Subject: Re: [PATCH] x86/Hyper-V: Support for free page reporting

On Wed, May 20, 2020 at 10:59:22AM +0200, Vitaly Kuznetsov wrote:
> Sunil Muthuswamy <sunilmut@...rosoft.com> writes:
[...]
> > +EXPORT_SYMBOL_GPL(hv_query_ext_cap);
> > diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> > index ebf34c7bc8bc..2de3f692c8bf 100644
> > --- a/arch/x86/kernel/cpu/mshyperv.c
> > +++ b/arch/x86/kernel/cpu/mshyperv.c
> > @@ -224,11 +224,13 @@ static void __init ms_hyperv_init_platform(void)
> >  	 * Extract the features and hints
> >  	 */
> >  	ms_hyperv.features = cpuid_eax(HYPERV_CPUID_FEATURES);
> > +	ms_hyperv.b_features = cpuid_ebx(HYPERV_CPUID_FEATURES);
> >  	ms_hyperv.misc_features = cpuid_edx(HYPERV_CPUID_FEATURES);
> >  	ms_hyperv.hints    = cpuid_eax(HYPERV_CPUID_ENLIGHTMENT_INFO);
> >  
> > -	pr_info("Hyper-V: features 0x%x, hints 0x%x, misc 0x%x\n",
> > -		ms_hyperv.features, ms_hyperv.hints, ms_hyperv.misc_features);
> > +	pr_info("Hyper-V: features 0x%x, additional features: 0x%x, hints 0x%x, misc 0x%x\n",
> > +		ms_hyperv.features, ms_hyperv.b_features, ms_hyperv.hints,
> > +		ms_hyperv.misc_features);
> 
> HYPERV_CPUID_FEATURES(0x40000003) EAX and EBX correspond to Partition
> Privilege Flags (TLFS), I'd suggest to take the opportunity and rename
> this to something like 'privilege flags low=0x%x high=0x%x'.
> 
> Also, I don't quite like 'ms_hyperv.b_features' as I'll always have to
> look at what it's being assigned to understand what it holds. I'd even
> suggest to rename ms_hyperv.features to ms_hyperv.priv_low and
> ms_hyperv.b_features tp ms_hyperv.priv_high. Or maybe even better, pack
> them to the same 'u64 ms_hyperv.privileges'.

+1 for this. :-)

Wei.