linux-kernel - [PATCH v6 1/4] KVM: x86: Clarify the kvm_run.emulation

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Date:   Mon, 20 Sep 2021 11:37:34 +0100
From:   David Edmondson <david.edmondson@...cle.com>
To:     linux-kernel@...r.kernel.org
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>, x86@...nel.org,
        Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...hat.com>,
        kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Sean Christopherson <seanjc@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Wanpeng Li <wanpengli@...cent.com>,
        David Matlack <dmatlack@...gle.com>,
        David Edmondson <david.edmondson@...cle.com>
Subject: [PATCH v6 1/4] KVM: x86: Clarify the kvm_run.emulation_failure structure layout

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@...gle.com>
Signed-off-by: David Edmondson <david.edmondson@...cle.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 a067410ebea5..8618fe973215 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 {
-- 
2.33.0