linux-kernel - [PATCH 1/2] KVM: x86: clear stale x86_emulate

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Date:   Tue,  3 Mar 2020 15:33:15 +0100
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org
Cc:     Jim Mattson <jmattson@...gle.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Bandan Das <bsd@...hat.com>, Oliver Upton <oupton@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] KVM: x86: clear stale x86_emulate_ctxt->intercept value

Commit c44b4c6ab80e ("KVM: emulate: clean up initializations in
init_decode_cache") reduced the number of fields cleared by
init_decode_cache() claiming that they are being cleared elsewhere,
'intercept', however, seems to be left uncleared in some cases.

The issue I'm observing manifests itself as following:
after commit 07721feee46b ("KVM: nVMX: Don't emulate instructions in guest
mode") Hyper-V guests on KVM stopped booting with:

 kvm_nested_vmexit:    rip fffff802987d6169 reason EPT_VIOLATION info1 181
    info2 0 int_info 0 int_info_err 0
 kvm_page_fault:       address febd0000 error_code 181
 kvm_emulate_insn:     0:fffff802987d6169: f3 a5
 kvm_emulate_insn:     0:fffff802987d6169: f3 a5 FAIL
 kvm_inj_exception:    #UD (0x0)

Fixes: c44b4c6ab80e ("KVM: emulate: clean up initializations in init_decode_cache")
Fixes: 07721feee46b ("KVM: nVMX: Don't emulate instructions in guest mode")
Cc: stable@...r.kernel.org
Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/emulate.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index dd19fb3539e0..bc00642e5d3b 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -5173,6 +5173,7 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
 	ctxt->fetch.ptr = ctxt->fetch.data;
 	ctxt->fetch.end = ctxt->fetch.data + insn_len;
 	ctxt->opcode_len = 1;
+	ctxt->intercept = x86_intercept_none;
 	if (insn_len > 0)
 		memcpy(ctxt->fetch.data, insn, insn_len);
 	else {
-- 
2.24.1