linux-kernel - Re: [PATCH 2/3] x86/kvm: Implement MSR

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Message-ID: <20180622190912.GG1882@zn.tnic>
Date:   Fri, 22 Jun 2018 21:09:12 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Radim Krčmář <rkrcmar@...hat.com>
Cc:     KVM <kvm@...r.kernel.org>, Joerg Roedel <joro@...tes.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Tony Luck <tony.luck@...el.com>,
        Yazen Ghannam <Yazen.Ghannam@....com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] x86/kvm: Implement MSR_HWCR support

On Fri, Jun 22, 2018 at 08:52:38PM +0200, Radim Krčmář wrote:
> msr_info->host_initiated is always going to return true, so it would be
> better to put it outside of __set_mci_status.
> 
> Maybe we could just write the whole logic inline, otherwise I'd call it
> something like mci_status_is_writeable.
> 
> >  static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >  {
> >  	u64 mcg_cap = vcpu->arch.mcg_cap;
> > @@ -2176,9 +2200,13 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
> >  			if ((offset & 0x3) == 0 &&
> >  			    data != 0 && (data | (1 << 10)) != ~(u64)0)
> >  				return -1;
> > -			if (!msr_info->host_initiated &&
> > -				(offset & 0x3) == 1 && data != 0)
> > -				return -1;
> > +
> > +			/* MCi_STATUS */
> > +			if ((offset & 0x3) == 1) {
> > +				if (!__set_mci_status(vcpu, msr_info))
> > +					return -1;
> > +			}
> 
> 			if (!msr_info->host_initiated &&
> 			    (offset & 0x3) == 1 && data != 0) {
> 				struct msr_data tmp = {.index = MSR_K7_HWCR};
> 
> 				if (!guest_cpuid_is_amd(vcpu) ||
> 				    !kvm_x86_ops->get_msr(vcpu, &tmp) ||
> 				    !(tmp.data & BIT_ULL(18)))
> 					return -1;

Don't you feel it is cleaner if all the MCi_STATUS checking is done in
a separate function? The indentation level and the bunch of checks in
set_msr_mce() make it hard to read while having a separate function
separates it and makes it easier to follow.

I mean, you're the maintainer but if I may give a suggestion, moving the
whole logic into a separate function would be more readable.

And then do:

	if (!msr_info->host_initiated) {
		if (check_mci_status(...))
			return -1;
	}

Something like that...

-- 
Regards/Gruss,
    Boris.

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