Re: [PATCH v3 03/34] KVM: x86: hyper-v: Add helper to read hypercall data for array

[Maxim Levitsky <mlevitsk@redhat.com>]

On Thu, 2022-04-14 at 15:19 +0200, Vitaly Kuznetsov wrote:
> From: Sean Christopherson <seanjc@google.com>
> 
> Move the guts of kvm_get_sparse_vp_set() to a helper so that the code for
> reading a guest-provided array can be reused in the future, e.g. for
> getting a list of virtual addresses whose TLB entries need to be flushed.
> 
> Opportunisticaly swap the order of the data and XMM adjustment so that
> the XMM/gpa offsets are bundled together.
> 
> No functional change intended.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
>  arch/x86/kvm/hyperv.c | 53 +++++++++++++++++++++++++++----------------
>  1 file changed, 33 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index fb716cf919ed..d66c27fd1e8a 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1758,38 +1758,51 @@ struct kvm_hv_hcall {
>  	sse128_t xmm[HV_HYPERCALL_MAX_XMM_REGISTERS];
>  };
>  
> -static u64 kvm_get_sparse_vp_set(struct kvm *kvm, struct kvm_hv_hcall *hc,
> -				 int consumed_xmm_halves,
> -				 u64 *sparse_banks, gpa_t offset)
> -{
> -	u16 var_cnt;
> -	int i;
>  
> -	if (hc->var_cnt > 64)
> -		return -EINVAL;
> -
> -	/* Ignore banks that cannot possibly contain a legal VP index. */
> -	var_cnt = min_t(u16, hc->var_cnt, KVM_HV_MAX_SPARSE_VCPU_SET_BITS);
> +static int kvm_hv_get_hc_data(struct kvm *kvm, struct kvm_hv_hcall *hc,
> +			      u16 orig_cnt, u16 cnt_cap, u64 *data,
> +			      int consumed_xmm_halves, gpa_t offset)
> +{
> +	/*
> +	 * Preserve the original count when ignoring entries via a "cap", KVM
> +	 * still needs to validate the guest input (though the non-XMM path
> +	 * punts on the checks).
> +	 */
> +	u16 cnt = min(orig_cnt, cnt_cap);
> +	int i, j;
>  
>  	if (hc->fast) {
>  		/*
>  		 * Each XMM holds two sparse banks, but do not count halves that
>  		 * have already been consumed for hypercall parameters.
>  		 */
> -		if (hc->var_cnt > 2 * HV_HYPERCALL_MAX_XMM_REGISTERS - consumed_xmm_halves)
> +		if (orig_cnt > 2 * HV_HYPERCALL_MAX_XMM_REGISTERS - consumed_xmm_halves)
>  			return HV_STATUS_INVALID_HYPERCALL_INPUT;
> -		for (i = 0; i < var_cnt; i++) {
> -			int j = i + consumed_xmm_halves;
> +
> +		for (i = 0; i < cnt; i++) {
> +			j = i + consumed_xmm_halves;
>  			if (j % 2)
> -				sparse_banks[i] = sse128_hi(hc->xmm[j / 2]);
> +				data[i] = sse128_hi(hc->xmm[j / 2]);
>  			else
> -				sparse_banks[i] = sse128_lo(hc->xmm[j / 2]);
> +				data[i] = sse128_lo(hc->xmm[j / 2]);
>  		}
>  		return 0;
>  	}
>  
> -	return kvm_read_guest(kvm, hc->ingpa + offset, sparse_banks,
> -			      var_cnt * sizeof(*sparse_banks));
> +	return kvm_read_guest(kvm, hc->ingpa + offset, data,
> +			      cnt * sizeof(*data));
> +}
> +
> +static u64 kvm_get_sparse_vp_set(struct kvm *kvm, struct kvm_hv_hcall *hc,
> +				 u64 *sparse_banks, int consumed_xmm_halves,
> +				 gpa_t offset)
> +{
> +	if (hc->var_cnt > 64)
> +		return -EINVAL;
> +
> +	/* Cap var_cnt to ignore banks that cannot contain a legal VP index. */
> +	return kvm_hv_get_hc_data(kvm, hc, hc->var_cnt, KVM_HV_MAX_SPARSE_VCPU_SET_BITS,
> +				  sparse_banks, consumed_xmm_halves, offset);
>  }
>  
>  static inline int hv_tlb_flush_ring_free(struct kvm_vcpu_hv *hv_vcpu,
> @@ -1937,7 +1950,7 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>  		if (!hc->var_cnt)
>  			goto ret_success;
>  
> -		if (kvm_get_sparse_vp_set(kvm, hc, 2, sparse_banks,
> +		if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks, 2,
>  					  offsetof(struct hv_tlb_flush_ex,
>  						   hv_vp_set.bank_contents)))
>  			return HV_STATUS_INVALID_HYPERCALL_INPUT;
> @@ -2048,7 +2061,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>  		if (!hc->var_cnt)
>  			goto ret_success;
>  
> -		if (kvm_get_sparse_vp_set(kvm, hc, 1, sparse_banks,
> +		if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks, 1,
>  					  offsetof(struct hv_send_ipi_ex,
>  						   vp_set.bank_contents)))
>  			return HV_STATUS_INVALID_HYPERCALL_INPUT;

I don't see anything wrong, but I don't know this area that well, so I might have
missed something.

Best regards,
	Maxim Levitsky