Re: [PATCH 0/4] KVM: x86: hyper-v: XMM fast hypercalls fixes

Vitaly Kuznetsov
2022-02-25T13:14:17Z

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 2/22/22 16:46, Vitaly Kuznetsov wrote:
>> While working on some Hyper-V TLB flush improvements and Direct TLB flush
>> feature for Hyper-V on KVM I experienced Windows Server 2019 crashes on
>> boot when XMM fast hypercall input feature is advertised. Turns out,
>> HVCALL_SEND_IPI_EX is also an XMM fast hypercall and returning an error
>> kills the guest. This is fixed in PATCH4. PATCH3 fixes erroneous capping
>> of sparse CPU banks for XMM fast TLB flush hypercalls. The problem should
>> be reproducible with >360 vCPUs.
>>
>> Vitaly Kuznetsov (4):
>> KVM: x86: hyper-v: Drop redundant 'ex' parameter from
>> kvm_hv_send_ipi()
>> KVM: x86: hyper-v: Drop redundant 'ex' parameter from
>> kvm_hv_flush_tlb()
>> KVM: x86: hyper-v: Fix the maximum number of sparse banks for XMM fast
>> TLB flush hypercalls
>> KVM: x86: hyper-v: HVCALL_SEND_IPI_EX is an XMM fast hypercall
>>
>> arch/x86/kvm/hyperv.c | 84 +++++++++++++++++++++++--------------------
>> 1 file changed, 45 insertions(+), 39 deletions(-)
>>
>
> Merging this in 5.18 is a bit messy. Please check that the below
> patch against kvm/next makes sense:

Something is wrong with the diff as it doesn't apply :-(

>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 653e08c993c4..98fb998c31ce 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1770,9 +1770,11 @@ struct kvm_hv_hcall {
> };
>
> 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;
> @@ -1780,13 +1782,29 @@ static u64 kvm_get_sparse_vp_set(struct kvm *kvm, struct kvm_hv_hcall *hc,
> /* 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);
>
> + 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)
> + return HV_STATUS_INVALID_HYPERCALL_INPUT;
> + for (i = 0; i < var_cnt; i++) {
> + int j = i + consumed_xmm_halves;
> + if (j % 2)
> + sparse_banks[i] = sse128_lo(hc->xmm[j / 2]);
> + else
> + sparse_banks[i] = sse128_hi(hc->xmm[j / 2]);

Let's say we have 1 half of XMM0 consumed. Now:

i = 0;
j = 1;
if (1)
sparse_banks[0] = sse128_lo(hc->xmm[0]);

This doesn't look right as we need to get the upper half of XMM0.

I guess it should be reversed,

if (j % 2)
sparse_banks[i] = sse128_hi(hc->xmm[j / 2]);
else
sparse_banks[i] = sse128_lo(hc->xmm[j / 2]);

> + }
> + return 0;
> + }
> +
> return kvm_read_guest(kvm, hc->ingpa + offset, sparse_banks,
> var_cnt * sizeof(*sparse_banks));
> }
>
> -static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool ex)
> +static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
> {
> - int i;
> struct kvm *kvm = vcpu->kvm;
> struct hv_tlb_flush_ex flush_ex;
> struct hv_tlb_flush flush;
> @@ -1803,7 +1821,8 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
> */
> BUILD_BUG_ON(KVM_HV_MAX_SPARSE_VCPU_SET_BITS > 64);
>
> - if (!ex) {
> + if (hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST ||
> + hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE) {

In case you're trying to come up with a smaller patch for 5.18, we can
certainly drop these 'ex'/'non-ex' changes as these are merely
cosmetic.

> if (hc->fast) {
> flush.address_space = hc->ingpa;
> flush.flags = hc->outgpa;
> @@ -1859,17 +1878,7 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
> if (!hc->var_cnt)
> goto ret_success;
>
> - if (hc->fast) {
> - if (hc->var_cnt > HV_HYPERCALL_MAX_XMM_REGISTERS - 1)
> - return HV_STATUS_INVALID_HYPERCALL_INPUT;
> - for (i = 0; i < hc->var_cnt; i += 2) {
> - sparse_banks[i] = sse128_lo(hc->xmm[i / 2 + 1]);
> - sparse_banks[i + 1] = sse128_hi(hc->xmm[i / 2 + 1]);
> - }
> - goto do_flush;
> - }
> -
> - if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks,
> + if (kvm_get_sparse_vp_set(kvm, hc, 2, sparse_banks,
> offsetof(struct hv_tlb_flush_ex,
> hv_vp_set.bank_contents)))

I like your idea to put 'consumed_xmm_halves' into
kvm_get_sparse_vp_set() as kvm_hv_flush_tlb is getting too big.

> return HV_STATUS_INVALID_HYPERCALL_INPUT;
> @@ -1913,7 +1922,7 @@ static void kvm_send_ipi_to_many(struct kvm *kvm, u32 vector,
> }
> }
>
> -static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool ex)
> +static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
> {
> struct kvm *kvm = vcpu->kvm;
> struct hv_send_ipi_ex send_ipi_ex;
> @@ -1924,7 +1933,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
> u32 vector;
> bool all_cpus;
>
> - if (!ex) {
> + if (hc->code == HVCALL_SEND_IPI) {
> if (!hc->fast) {
> if (unlikely(kvm_read_guest(kvm, hc->ingpa, &send_ipi,
> sizeof(send_ipi))))
> @@ -1943,9 +1952,15 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
>
> 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,
> @@ -1964,7 +1979,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
> if (!hc->var_cnt)
> goto ret_success;
>
> - if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks,
> + if (kvm_get_sparse_vp_set(kvm, hc, 1, sparse_banks,
> offsetof(struct hv_send_ipi_ex,
> vp_set.bank_contents)))
> return HV_STATUS_INVALID_HYPERCALL_INPUT;
> @@ -2126,6 +2141,7 @@ 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;
> }
>
> @@ -2283,46 +2299,43 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
> kvm_hv_hypercall_complete_userspace;
> return 0;
> case HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST:
> - if (unlikely(!hc.rep_cnt || hc.rep_idx || hc.var_cnt)) {
> + if (unlikely(hc.var_cnt)) {
> ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> break;
> }
> - ret = kvm_hv_flush_tlb(vcpu, &hc, false);
> - break;
> - case HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE:
> - if (unlikely(hc.rep || hc.var_cnt)) {
> - ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> - break;
> - }
> - ret = kvm_hv_flush_tlb(vcpu, &hc, false);
> - break;
> + fallthrough;
> case HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST_EX:
> if (unlikely(!hc.rep_cnt || hc.rep_idx)) {
> ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> break;
> }
> - ret = kvm_hv_flush_tlb(vcpu, &hc, true);
> + ret = kvm_hv_flush_tlb(vcpu, &hc);
> break;
> + case HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE:
> + if (unlikely(hc.var_cnt)) {
> + ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> + break;
> + }
> + fallthrough;
> case HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX:
> if (unlikely(hc.rep)) {
> ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> break;
> }
> - ret = kvm_hv_flush_tlb(vcpu, &hc, true);
> + ret = kvm_hv_flush_tlb(vcpu, &hc);
> break;
> case HVCALL_SEND_IPI:
> - if (unlikely(hc.rep || hc.var_cnt)) {
> + if (unlikely(hc.var_cnt)) {
> ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> break;
> }
> - ret = kvm_hv_send_ipi(vcpu, &hc, false);
> - break;
> + fallthrough;
> case HVCALL_SEND_IPI_EX:
> - if (unlikely(hc.fast || hc.rep)) {
> + if (unlikely(hc.rep)) {
> ret = HV_STATUS_INVALID_HYPERCALL_INPUT;
> break;
> }
> - ret = kvm_hv_send_ipi(vcpu, &hc, true);
> + ret = kvm_hv_send_ipi(vcpu, &hc);
> break;
> case HVCALL_POST_DEBUG_DATA:
> case HVCALL_RETRIEVE_DEBUG_DATA:

I've smoke tested this (with the change I've mentioned above) and WS2019
booted with 65 vCPUs. This is a good sign)

>
>
> The resulting merge commit is already in kvm/queue shortly (which should
> become the next kvm/next as soon as tests complete).
>

I see, please swap sse128_lo()/sse128_hi() there too :-)

--
Vitaly