linux-kernel - Re: [PATCH 02/61] KVM: x86: Refactor loop around do_cpuid

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Date:   Thu, 06 Feb 2020 15:59:49 +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 02/61] KVM: x86: Refactor loop around do_cpuid_func() to separate helper

Sean Christopherson <sean.j.christopherson@...el.com> writes:

> Move the guts of kvm_dev_ioctl_get_cpuid()'s CPUID func loop to a
> separate helper to improve code readability and pave the way for future
> cleanup.
>
> No functional change intended.
>
> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
> ---
>  arch/x86/kvm/cpuid.c | 45 ++++++++++++++++++++++++++------------------
>  1 file changed, 27 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 47ce04762c20..f49fdd06f511 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -839,6 +839,29 @@ static bool is_centaur_cpu(const struct kvm_cpuid_param *param)
>  	return boot_cpu_data.x86_vendor == X86_VENDOR_CENTAUR;
>  }
>  
> +static int get_cpuid_func(struct kvm_cpuid_entry2 *entries, u32 func,
> +			  int *nent, int maxnent, unsigned int type)
> +{
> +	u32 limit;
> +	int r;
> +
> +	r = do_cpuid_func(&entries[*nent], func, nent, maxnent, type);
> +	if (r)
> +		return r;
> +
> +	limit = entries[*nent - 1].eax;
> +	for (func = func + 1; func <= limit; ++func) {
> +		if (*nent >= maxnent)
> +			return -E2BIG;
> +
> +		r = do_cpuid_func(&entries[*nent], func, nent, maxnent, type);
> +		if (r)
> +			break;
> +	}
> +
> +	return r;
> +}
> +
>  static bool sanity_check_entries(struct kvm_cpuid_entry2 __user *entries,
>  				 __u32 num_entries, unsigned int ioctl_type)
>  {
> @@ -871,8 +894,8 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
>  			    unsigned int type)
>  {
>  	struct kvm_cpuid_entry2 *cpuid_entries;
> -	int limit, nent = 0, r = -E2BIG, i;
> -	u32 func;
> +	int nent = 0, r = -E2BIG, i;

Not this patches fault, but I just noticed that '-E2BIG' initializer
here is only being used for 

 'if (cpuid->nent < 1)'

case so I have two suggestion:
1) Return directly without the 'goto' , drop the initializer.
2) Return -EINVAL instead.

> +
>  	static const struct kvm_cpuid_param param[] = {
>  		{ .func = 0 },
>  		{ .func = 0x80000000 },
> @@ -901,22 +924,8 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
>  		if (ent->qualifier && !ent->qualifier(ent))
>  			continue;
>  
> -		r = do_cpuid_func(&cpuid_entries[nent], ent->func,
> -				  &nent, cpuid->nent, type);
> -
> -		if (r)
> -			goto out_free;
> -
> -		limit = cpuid_entries[nent - 1].eax;
> -		for (func = ent->func + 1; func <= limit && r == 0; ++func) {
> -			if (nent >= cpuid->nent) {
> -				r = -E2BIG;
> -				goto out_free;
> -			}
> -			r = do_cpuid_func(&cpuid_entries[nent], func,
> -				          &nent, cpuid->nent, type);
> -		}
> -
> +		r = get_cpuid_func(cpuid_entries, ent->func, &nent,
> +				   cpuid->nent, type);
>  		if (r)
>  			goto out_free;
>  	}

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>

-- 
Vitaly