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From:   David Edmondson <david.edmondson@oracle.com>
To:     linux-kernel@vger.kernel.org
Cc:     Jim Mattson <jmattson@google.com>, Borislav Petkov <bp@alien8.de>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Wanpeng Li <wanpengli@tencent.com>,
        Ingo Molnar <mingo@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        David Matlack <dmatlack@google.com>, x86@kernel.org,
        kvm@vger.kernel.org, David Edmondson <david.edmondson@oracle.com>
Subject: [PATCH v4 1/4] KVM: x86: Clarify the kvm_run.emulation_failure structure layout
Date:   Fri, 13 Aug 2021 08:12:08 +0100
Message-Id: <20210813071211.1635310-2-david.edmondson@oracle.com>
In-Reply-To: <20210813071211.1635310-1-david.edmondson@oracle.com>
References: <20210813071211.1635310-1-david.edmondson@oracle.com>
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Until more flags for kvm_run.emulation_failure flags are defined, it
is undetermined whether new payload elements corresponding to those
flags will be additive or alternative. As a hint to userspace that an
alternative is possible, wrap the current payload elements in a union.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Edmondson <david.edmondson@oracle.com>
---
 include/uapi/linux/kvm.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index d9e4aabcb31a..6c79c1ce3703 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -402,8 +402,12 @@ struct kvm_run {
 			__u32 suberror;
 			__u32 ndata;
 			__u64 flags;
-			__u8  insn_size;
-			__u8  insn_bytes[15];
+			union {
+				struct {
+					__u8  insn_size;
+					__u8  insn_bytes[15];
+				};
+			};
 		} emulation_failure;
 		/* KVM_EXIT_OSI */
 		struct {
-- 
2.30.2