linux-kernel - Re: [PATCH 03/61] KVM: x86: Simplify handling of Centaur CPUID leafs

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Date:   Fri, 7 Feb 2020 11:47:02 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH 03/61] KVM: x86: Simplify handling of Centaur CPUID leafs

On Thu, Feb 06, 2020 at 04:05:54PM +0100, Vitaly Kuznetsov wrote:
> Sean Christopherson <sean.j.christopherson@...el.com> writes:
> 
> > Refactor the handling of the Centaur-only CPUID leaf to detect the leaf
> > via a runtime query instead of adding a one-off callback in the static
> > array.  When the callback was introduced, there were additional fields
> > in the array's structs, and more importantly, retpoline wasn't a thing.
> >
> > No functional change intended.
> >
> > Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> > ---
> >  arch/x86/kvm/cpuid.c | 32 ++++++++++----------------------
> >  1 file changed, 10 insertions(+), 22 deletions(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index f49fdd06f511..de52cbb46171 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -829,15 +829,7 @@ static int do_cpuid_func(struct kvm_cpuid_entry2 *entry, u32 func,
> >  	return __do_cpuid_func(entry, func, nent, maxnent);
> >  }
> >  
> > -struct kvm_cpuid_param {
> > -	u32 func;
> > -	bool (*qualifier)(const struct kvm_cpuid_param *param);
> > -};
> > -
> > -static bool is_centaur_cpu(const struct kvm_cpuid_param *param)
> > -{
> > -	return boot_cpu_data.x86_vendor == X86_VENDOR_CENTAUR;
> > -}
> > +#define CENTAUR_CPUID_SIGNATURE 0xC0000000
> 
> arch/x86/kernel/cpu/centaur.c also hardcodes the value, would make sense
> to put it to some x86 header instead.

Ya, I just didn't want to touch non-KVM code in a 60+ patch series.

> >  static int get_cpuid_func(struct kvm_cpuid_entry2 *entries, u32 func,
> >  			  int *nent, int maxnent, unsigned int type)
> > @@ -845,6 +837,10 @@ static int get_cpuid_func(struct kvm_cpuid_entry2 *entries, u32 func,
> >  	u32 limit;
> >  	int r;
> >  
> > +	if (func == CENTAUR_CPUID_SIGNATURE &&
> > +	    boot_cpu_data.x86_vendor != X86_VENDOR_CENTAUR)
> > +		return 0;
> > +
> >  	r = do_cpuid_func(&entries[*nent], func, nent, maxnent, type);
> >  	if (r)
> >  		return r;
> > @@ -896,11 +892,8 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
> >  	struct kvm_cpuid_entry2 *cpuid_entries;
> >  	int nent = 0, r = -E2BIG, i;
> >  
> > -	static const struct kvm_cpuid_param param[] = {
> > -		{ .func = 0 },
> > -		{ .func = 0x80000000 },
> > -		{ .func = 0xC0000000, .qualifier = is_centaur_cpu },
> > -		{ .func = KVM_CPUID_SIGNATURE },
> > +	static const u32 funcs[] = {
> > +		0, 0x80000000, CENTAUR_CPUID_SIGNATURE, KVM_CPUID_SIGNATURE,
> >  	};
> >  
> >  	if (cpuid->nent < 1)
> > @@ -918,14 +911,9 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
> >  		goto out;
> >  
> >  	r = 0;
> > -	for (i = 0; i < ARRAY_SIZE(param); i++) {
> > -		const struct kvm_cpuid_param *ent = &param[i];
> > -
> > -		if (ent->qualifier && !ent->qualifier(ent))
> > -			continue;
> > -
> > -		r = get_cpuid_func(cpuid_entries, ent->func, &nent,
> > -				   cpuid->nent, type);
> > +	for (i = 0; i < ARRAY_SIZE(funcs); i++) {
> > +		r = get_cpuid_func(cpuid_entries, funcs[i], &nent, cpuid->nent,
> > +				   type);
> >  		if (r)
> >  			goto out_free;
> >  	}
> 
> Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> 
> -- 
> Vitaly
>