[Devel] [PATCH RHEL7 COMMIT] ms/KVM: x86: set ctxt->have_exception in x86_decode_insn()

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-957.27.2.vz7.107.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-957.27.2.vz7.107.13
------>
commit 0233d7fda444bf90759fcaec1dbd810c2298eb1d
Author: Jan Dakinevich <jan.dakinevich at virtuozzo.com>
Date:   Thu Oct 3 15:03:47 2019 +0300

    ms/KVM: x86: set ctxt->have_exception in x86_decode_insn()
    
    x86_emulate_instruction() takes into account ctxt->have_exception flag
    during instruction decoding, but in practice this flag is never set in
    x86_decode_insn().
    
    Fixes: 6ea6e84309ca ("KVM: x86: inject exceptions produced by x86_decode_insn")
    Cc: stable at vger.kernel.org
    Cc: Denis Lunev <den at virtuozzo.com>
    Cc: Roman Kagan <rkagan at virtuozzo.com>
    Cc: Denis Plotnikov <dplotnikov at virtuozzo.com>
    Signed-off-by: Jan Dakinevich <jan.dakinevich at virtuozzo.com>
    
    Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
    
    https://jira.sw.ru/browse/PSBM-68018
    (cherry-picked from c8848cee74ff05638e913582a476bde879c968ad)
    
    =====================
    Patchset description:
    
    fix emulation error on Windows bootup
    
    This series intended to fix (again) a bug that was a subject of the
    following change:
    
      6ea6e84 ("KVM: x86: inject exceptions produced by x86_decode_insn")
    
    Suddenly, that fix had a couple mistakes. First, ctxt->have_exception was
    not set if fault happened during instruction decoding. Second, returning
    value of inject_emulated_instruction was used to make the decision to
    reenter guest, but this could happen iff on nested page fault, that is not
    the scope where this bug could occur.
    
    https://lkml.org/lkml/2019/8/29/152
    
    Jan Dakinevich (2):
      KVM: x86: always stop emulation on page fault
      KVM: x86: set ctxt->have_exception in x86_decode_insn()
    
    Paolo Bonzini (1):
      KVM: x86: inject exceptions produced by x86_decode_insn
---
 arch/x86/kvm/emulate.c | 2 ++
 arch/x86/kvm/x86.c     | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 94898cd05857..93d2203a7942 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -5311,6 +5311,8 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len)
 					ctxt->memopp->addr.mem.ea + ctxt->_eip);
 
 done:
+	if (rc == X86EMUL_PROPAGATE_FAULT)
+		ctxt->have_exception = true;
 	return (rc != X86EMUL_CONTINUE) ? EMULATION_FAILED : EMULATION_OK;
 }
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8ed5b23ff055..980d469f3f63 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5760,6 +5760,12 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu,
 						emulation_type))
 				return EMULATE_DONE;
 			if (ctxt->have_exception) {
+				/*
+				 * #UD should result in just EMULATION_FAILED, and trap-like
+				 * exception should not be encountered during decode.
+				 */
+				WARN_ON_ONCE(ctxt->exception.vector == UD_VECTOR ||
+					     exception_type(ctxt->exception.vector) == EXCPT_TRAP);
 				inject_emulated_exception(vcpu);
 				return EMULATE_DONE;
 			}