Re: [PATCH v9 2/6] x86/kvm/hyper-v: Simplify addition for custom cpuid leafs

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Jon Doron <arilou@gmail.com> writes:

> Simlify the code to define a new cpuid leaf group by enabled feature.
>
> This also fixes a bug in which the max cpuid leaf was always set to
> HYPERV_CPUID_NESTED_FEATURES regardless if nesting is supported or not.
>
> Any new CPUID group needs to consider the max leaf and be added in the
> correct order, in this method there are two rules:
> 1. Each cpuid leaf group must be order in an ascending order
> 2. The appending for the cpuid leafs by features also needs to happen by
>    ascending order.
>
> Signed-off-by: Jon Doron <arilou@gmail.com>
> ---
>  arch/x86/kvm/hyperv.c | 46 ++++++++++++++++++++++++++++++-------------
>  1 file changed, 32 insertions(+), 14 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index a86fda7a1d03..7383c7e7d4af 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1785,27 +1785,45 @@ int kvm_vm_ioctl_hv_eventfd(struct kvm *kvm, struct kvm_hyperv_eventfd *args)
>  	return kvm_hv_eventfd_assign(kvm, args->conn_id, args->fd);
>  }
>  
> +// Must be sorted in ascending order by function

scripts/checkpatch.pl should've complained here, kernel coding style
always requires /* */ 

> +static struct kvm_cpuid_entry2 core_cpuid_entries[] = {
> +	{ .function = HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS },
> +	{ .function = HYPERV_CPUID_INTERFACE },
> +	{ .function = HYPERV_CPUID_VERSION },
> +	{ .function = HYPERV_CPUID_FEATURES },
> +	{ .function = HYPERV_CPUID_ENLIGHTMENT_INFO },
> +	{ .function = HYPERV_CPUID_IMPLEMENT_LIMITS },
> +};
> +
> +static struct kvm_cpuid_entry2 evmcs_cpuid_entries[] = {
> +	{ .function = HYPERV_CPUID_NESTED_FEATURES },
> +};
> +
> +#define HV_MAX_CPUID_ENTRIES \
> +	ARRAY_SIZE(core_cpuid_entries) +\
> +	ARRAY_SIZE(evmcs_cpuid_entries)
> +
>  int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>  				struct kvm_cpuid_entry2 __user *entries)
>  {
>  	uint16_t evmcs_ver = 0;
> -	struct kvm_cpuid_entry2 cpuid_entries[] = {
> -		{ .function = HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS },
> -		{ .function = HYPERV_CPUID_INTERFACE },
> -		{ .function = HYPERV_CPUID_VERSION },
> -		{ .function = HYPERV_CPUID_FEATURES },
> -		{ .function = HYPERV_CPUID_ENLIGHTMENT_INFO },
> -		{ .function = HYPERV_CPUID_IMPLEMENT_LIMITS },
> -		{ .function = HYPERV_CPUID_NESTED_FEATURES },
> -	};
> -	int i, nent = ARRAY_SIZE(cpuid_entries);
> +	struct kvm_cpuid_entry2 cpuid_entries[HV_MAX_CPUID_ENTRIES];
> +	int i, nent = 0;
> +
> +	/* Set the core cpuid entries required for Hyper-V */
> +	memcpy(&cpuid_entries[nent], &core_cpuid_entries,
> +	       sizeof(core_cpuid_entries));
> +	nent += ARRAY_SIZE(core_cpuid_entries);

Strictly speaking "+=" is not needed here as nent is zero.

>  
>  	if (kvm_x86_ops->nested_get_evmcs_version)
>  		evmcs_ver = kvm_x86_ops->nested_get_evmcs_version(vcpu);
>  
> -	/* Skip NESTED_FEATURES if eVMCS is not supported */
> -	if (!evmcs_ver)
> -		--nent;
> +	if (evmcs_ver) {
> +		/* EVMCS is enabled, add the required EVMCS CPUID leafs */
> +		memcpy(&cpuid_entries[nent], &evmcs_cpuid_entries,
> +		       sizeof(evmcs_cpuid_entries));
> +		nent += ARRAY_SIZE(evmcs_cpuid_entries);
> +	}
>  
>  	if (cpuid->nent < nent)
>  		return -E2BIG;
> @@ -1821,7 +1839,7 @@ int kvm_vcpu_ioctl_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
>  		case HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS:
>  			memcpy(signature, "Linux KVM Hv", 12);
>  
> -			ent->eax = HYPERV_CPUID_NESTED_FEATURES;
> +			ent->eax = cpuid_entries[nent - 1].function;
>  			ent->ebx = signature[0];
>  			ent->ecx = signature[1];
>  			ent->edx = signature[2];

With the nitpicks mentioned above:

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

-- 
Vitaly