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

Paolo Bonzini
2022-02-25T11:55:16Z

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:

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]);
+ }
+ 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) {
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)))
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:

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

Paolo