Re: [PATCH 4/4] KVM: x86: hyper-v: HVCALL_SEND_IPI_EX is an XMM fast hypercall

Maxim Levitsky
2022-02-25T18:34:05Z

On Tue, 2022-02-22 at 16:46 +0100, Vitaly Kuznetsov wrote:
> It has been proven on practice that at least Windows Server 2019 tries
> using HVCALL_SEND_IPI_EX in 'XMM fast' mode when it has more than 64 vCPUs
> and it needs to send an IPI to a vCPU > 63. Similarly to other XMM Fast
> hypercalls (HVCALL_FLUSH_VIRTUAL_ADDRESS_{LIST,SPACE}{,_EX}), this
> information is missing in TLFS as of 6.0b. Currently, KVM returns an error
> (HV_STATUS_INVALID_HYPERCALL_INPUT) and Windows crashes.
>
> Note, HVCALL_SEND_IPI is a 'standard' fast hypercall (not 'XMM fast') as
> all its parameters fit into RDX:R8 and this is handled by KVM correctly.
>
> Fixes: d8f5537a8816 ("KVM: hyper-v: Advertise support for fast XMM hypercalls")
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/kvm/hyperv.c | 52 ++++++++++++++++++++++++++++---------------
> 1 file changed, 34 insertions(+), 18 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 6dda93bf98ae..3060057bdfd4 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1890,6 +1890,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
> int sparse_banks_len;
> u32 vector;
> bool all_cpus;
> + int i;
>
> if (hc->code == HVCALL_SEND_IPI) {
> if (!hc->fast) {
> @@ -1910,9 +1911,15 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>
> trace_kvm_hv_send_ipi(vector, sparse_banks[0]);
> } else {
> - if (unlikely(kvm_read_guest(kvm, hc->ingpa, &send_ipi_ex,
> - sizeof(send_ipi_ex))))
> - return HV_STATUS_INVALID_HYPERCALL_INPUT;
> + if (!hc->fast) {
> + if (unlikely(kvm_read_guest(kvm, hc->ingpa, &send_ipi_ex,
> + sizeof(send_ipi_ex))))
> + return HV_STATUS_INVALID_HYPERCALL_INPUT;
> + } else {
> + send_ipi_ex.vector = (u32)hc->ingpa;
> + send_ipi_ex.vp_set.format = hc->outgpa;
> + send_ipi_ex.vp_set.valid_bank_mask = sse128_lo(hc->xmm[0]);
> + }
>
> trace_kvm_hv_send_ipi_ex(send_ipi_ex.vector,
> send_ipi_ex.vp_set.format,
> @@ -1920,8 +1927,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
>
> vector = send_ipi_ex.vector;
> valid_bank_mask = send_ipi_ex.vp_set.valid_bank_mask;
> - sparse_banks_len = bitmap_weight(&valid_bank_mask, 64) *
> - sizeof(sparse_banks[0]);
> + sparse_banks_len = bitmap_weight(&valid_bank_mask, 64);
Is this change intentional?

I haven't fully reviewed this, because kvm/queue seem to have a bit different
version of this, and I didn't fully follow on all of this.

Best regards,
Maxim Levitsky

>
> all_cpus = send_ipi_ex.vp_set.format == HV_GENERIC_SET_ALL;
>
> @@ -1931,12 +1937,27 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
> if (!sparse_banks_len)
> goto ret_success;
>
> - if (kvm_read_guest(kvm,
> - hc->ingpa + offsetof(struct hv_send_ipi_ex,
> - vp_set.bank_contents),
> - sparse_banks,
> - sparse_banks_len))
> - return HV_STATUS_INVALID_HYPERCALL_INPUT;
> + if (!hc->fast) {
> + if (kvm_read_guest(kvm,
> + hc->ingpa + offsetof(struct hv_send_ipi_ex,
> + vp_set.bank_contents),
> + sparse_banks,
> + sparse_banks_len * sizeof(sparse_banks[0])))
> + return HV_STATUS_INVALID_HYPERCALL_INPUT;
> + } else {
> + /*
> + * The lower half of XMM0 is already consumed, each XMM holds
> + * two sparse banks.
> + */
> + if (sparse_banks_len > (2 * HV_HYPERCALL_MAX_XMM_REGISTERS - 1))
> + return HV_STATUS_INVALID_HYPERCALL_INPUT;
> + for (i = 0; i < sparse_banks_len; i++) {
> + if (i % 2)
> + sparse_banks[i] = sse128_lo(hc->xmm[(i + 1) / 2]);
> + else
> + sparse_banks[i] = sse128_hi(hc->xmm[i / 2]);
> + }
> + }
> }
>
> check_and_send_ipi:
> @@ -2098,6 +2119,7 @@ static bool is_xmm_fast_hypercall(struct kvm_hv_hcall *hc)
> case HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE:
> case HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX:
> case HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX:
> + case HVCALL_SEND_IPI_EX:
> return true;
> }
>
> @@ -2265,14 +2287,8 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> ret = kvm_hv_flush_tlb(vcpu, &hc);
> break;
> case HVCALL_SEND_IPI:
> - if (unlikely(hc.rep)) {
> - ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> - break;
> - }
> - ret = kvm_hv_send_ipi(vcpu, &hc);
> - break;
> case HVCALL_SEND_IPI_EX:
> - if (unlikely(hc.fast || hc.rep)) {
> + if (unlikely(hc.rep)) {
> ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> break;
> }