FAILED: patch "[PATCH] KVM: x86: Ignore sparse banks size for an "all CPUs"," failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 3244867af8c065e51969f1bffe732d3ebfd9a7d2 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <[email protected]>
Date: Tue, 7 Dec 2021 22:09:19 +0000
Subject: [PATCH] KVM: x86: Ignore sparse banks size for an "all CPUs",
non-sparse IPI req

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.

Message-Id: <[email protected]>

index 5e19e6e4c2ce..8d8c1cc7cb53 100644
@@ -1922,11 +1922,13 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
 
 		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,
 				   hc->ingpa + offsetof(struct hv_send_ipi_ex,
 							vp_set.bank_contents),
 				   sparse_banks,

@@ -1934,6 +1936,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc, bool
 			return HV_STATUS_INVALID_HYPERCALL_INPUT;
 	}
 
+check_and_send_ipi:
 	if ((vector < HV_IPI_LOW_VECTOR) || (vector > HV_IPI_HIGH_VECTOR))
 		return HV_STATUS_INVALID_HYPERCALL_INPUT;