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

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Date:   Thu, 06 Feb 2020 16:05:54 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.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

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.

>  
>  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