Re: [PATCH] KVM: Refactor and simplify kvm_dev_ioctl_get_supported_cpuid

[Avi Kivity <avi@redhat.com>]

On 11/25/2011 10:12 AM, Sasha Levin wrote:
> This patch cleans and simplifies kvm_dev_ioctl_get_supported_cpuid by using a table
> instead of duplicating code as Avi suggested.
>
> This patch also fixes a bug where kvm_dev_ioctl_get_supported_cpuid would return
> -E2BIG when amount of entries passed was just right.
>
> Cc: Avi Kivity <avi@redhat.com>
> Cc: Marcelo Tosatti <mtosatti@redhat.com>
> Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
> ---
>  arch/x86/kvm/cpuid.c |   78 ++++++++++++++++++++++---------------------------
>  1 files changed, 35 insertions(+), 43 deletions(-)
>
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index bbaa6d8..c9ede4d 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -425,12 +425,31 @@ static void do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  
>  #undef F
>  
> +struct kvm_cpuid_param {
> +	u32 func;
> +	u32 idx;
> +	u32 leaves;

What does 'leaves' mean?  That it has a leaf count in eax?  if so it
want a better name and to be a bool.

> +	int (*qualifier)(struct kvm_cpuid_param *param);

bool

> +};
> +
> +int is_centaur_cpu(struct kvm_cpuid_param *param)
> +{
> +	return boot_cpu_data.x86_vendor == X86_VENDOR_CENTAUR;
> +}
> +
static

>  int kvm_dev_ioctl_get_supported_cpuid(struct kvm_cpuid2 *cpuid,
>  				      struct kvm_cpuid_entry2 __user *entries)
>  {
>  	struct kvm_cpuid_entry2 *cpuid_entries;
> -	int limit, nent = 0, r = -E2BIG;
> +	int limit, nent = 0, r = -E2BIG, i;
>  	u32 func;
> +	struct kvm_cpuid_param param[] = {
> +		{ .func = 0, .leaves = 1 },
> +		{ .func = 0x80000000, .leaves = 1 },
> +		{ .func = 0xC0000000, .qualifier = is_centaur_cpu, .leaves = 1 },
> +		{ .func = KVM_CPUID_SIGNATURE },
> +		{ .func = KVM_CPUID_FEATURES },
> +	};

static

>  
>  	if (cpuid->nent < 1)
>  		goto out;
> @@ -441,59 +460,32 @@ int kvm_dev_ioctl_get_supported_cpuid(struct kvm_cpuid2 *cpuid,
>  	if (!cpuid_entries)
>  		goto out;
>  
> -	do_cpuid_ent(&cpuid_entries[0], 0, 0, &nent, cpuid->nent);
> -	limit = cpuid_entries[0].eax;
> -	for (func = 1; func <= limit && nent < cpuid->nent; ++func)
> -		do_cpuid_ent(&cpuid_entries[nent], func, 0,
> -			     &nent, cpuid->nent);
> -	r = -E2BIG;
> -	if (nent >= cpuid->nent)
> -		goto out_free;
> -
> -	do_cpuid_ent(&cpuid_entries[nent], 0x80000000, 0, &nent, cpuid->nent);
> -	limit = cpuid_entries[nent - 1].eax;
> -	for (func = 0x80000001; func <= limit && nent < cpuid->nent; ++func)
> -		do_cpuid_ent(&cpuid_entries[nent], func, 0,
> -			     &nent, cpuid->nent);
> -
> +	for (i = 0; i < ARRAY_SIZE(param); i++) {
> +		struct kvm_cpuid_param *ent = &param[i];
>  
> +		if (ent->qualifier && !ent->qualifier(ent))
> +			continue;
>  
> -	r = -E2BIG;
> -	if (nent >= cpuid->nent)
> -		goto out_free;
> +		if (nent >= cpuid->nent)
> +			break;
>  
> -	/* Add support for Centaur's CPUID instruction. */
> -	if (boot_cpu_data.x86_vendor == X86_VENDOR_CENTAUR) {
> -		do_cpuid_ent(&cpuid_entries[nent], 0xC0000000, 0,
> +		do_cpuid_ent(&cpuid_entries[nent], ent->func, ent->idx,
>  				&nent, cpuid->nent);
>  
> -		r = -E2BIG;
> -		if (nent >= cpuid->nent)
> -			goto out_free;
> +		if (!ent->leaves)
> +			continue;
>  
>  		limit = cpuid_entries[nent - 1].eax;
> -		for (func = 0xC0000001;
> -			func <= limit && nent < cpuid->nent; ++func)
> -			do_cpuid_ent(&cpuid_entries[nent], func, 0,
> -					&nent, cpuid->nent);
> +		for (func = ent->func + 1; func <= limit && nent < cpuid->nent; ++func)
> +			do_cpuid_ent(&cpuid_entries[nent], func, ent->idx,
> +				     &nent, cpuid->nent);
>  
> -		r = -E2BIG;
> -		if (nent >= cpuid->nent)
> -			goto out_free;
> +		if (func <= limit)
> +			break;
>  	}
>  
> -	do_cpuid_ent(&cpuid_entries[nent], KVM_CPUID_SIGNATURE, 0, &nent,
> -		     cpuid->nent);
> -
> -	r = -E2BIG;
> -	if (nent >= cpuid->nent)
> -		goto out_free;
> -
> -	do_cpuid_ent(&cpuid_entries[nent], KVM_CPUID_FEATURES, 0, &nent,
> -		     cpuid->nent);
> -
>  	r = -E2BIG;
> -	if (nent >= cpuid->nent)
> +	if (i < ARRAY_SIZE(param) || nent > cpuid->nent)
>  		goto out_free;
>  

Isn't the first condition sufficient?

The code may be more readable if do_cpuid_ent() (and do_cpuid_1_ent)
returned -E2BIG on overflow instead of all this cleverness.

-- 
error compiling committee.c: too many arguments to function