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Subject[PATCH 5.10 15/33] KVM: x86: Ignore sparse banks size for an "all CPUs", non-sparse IPI req
From: Sean Christopherson <>

commit 3244867af8c065e51969f1bffe732d3ebfd9a7d2 upstream.

Do not bail early if there are no bits set in the sparse banks for a
non-sparse, a.k.a. "all CPUs", IPI request. Per the Hyper-V spec, it is
legal to have a variable length of '0', e.g. VP_SET's BankContents in
this case, if the request can be serviced without the extra info.

It is possible that for a given invocation of a hypercall that does
accept variable sized input headers that all the header input fits
entirely within the fixed size header. In such cases the variable sized
input header is zero-sized and the corresponding bits in the hypercall
input should be set to zero.

Bailing early results in KVM failing to send IPIs to all CPUs as expected
by the guest.

Fixes: 214ff83d4473 ("KVM: x86: hyperv: implement PV IPI send hypercalls")
Signed-off-by: Sean Christopherson <>
Reviewed-by: Vitaly Kuznetsov <>
Message-Id: <>
Signed-off-by: Paolo Bonzini <>
Signed-off-by: Vitaly Kuznetsov <>
Signed-off-by: Greg Kroah-Hartman <>
arch/x86/kvm/hyperv.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1641,11 +1641,13 @@ static u64 kvm_hv_send_ipi(struct kvm_vc

all_cpus = send_ipi_ex.vp_set.format == HV_GENERIC_SET_ALL;

+ if (all_cpus)
+ goto check_and_send_ipi;
if (!sparse_banks_len)
goto ret_success;

- if (!all_cpus &&
- kvm_read_guest(kvm,
+ if (kvm_read_guest(kvm,
ingpa + offsetof(struct hv_send_ipi_ex,
@@ -1653,6 +1655,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vc

if ((vector < HV_IPI_LOW_VECTOR) || (vector > HV_IPI_HIGH_VECTOR))

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