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

Maxim Levitsky
2022-05-11T11:21:15Z

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