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

Vitaly Kuznetsov
2022-02-28T10:03:32Z

Maxim Levitsky <mlevitsk@redhat.com> writes:

> 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?
>

Yes it is. Previously, 'sparse_banks_len' was the number of bytes to
read, now it's in u64-s.

(see below)

> 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.
>
>>
>> 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])))

^^^ here ^^^

>> + 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;

And here. This is the reason for change: it's more convenient to count
it 'xmm halves' than in bytes.

>> + 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;
>> }
>
>

--
Vitaly