4.20-stable review patch. If anyone has any objections, please let me know.
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From: Alexander Popov alex.popov@linux.com
commit 5cc244a20b86090c087073c124284381cdf47234 upstream.
The single-step debugging of KVM guests on x86 is broken: if we run gdb 'stepi' command at the breakpoint when the guest interrupts are enabled, RIP always jumps to native_apic_mem_write(). Then other nasty effects follow.
Long investigation showed that on Jun 7, 2017 the commit c8401dda2f0a00cd25c0 ("KVM: x86: fix singlestepping over syscall") introduced the kvm_run.debug corruption: kvm_vcpu_do_singlestep() can be called without X86_EFLAGS_TF set.
Let's fix it. Please consider that for -stable.
Signed-off-by: Alexander Popov alex.popov@linux.com Cc: stable@vger.kernel.org Fixes: c8401dda2f0a00cd25c0 ("KVM: x86: fix singlestepping over syscall") Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kvm/x86.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
--- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6407,8 +6407,7 @@ restart: toggle_interruptibility(vcpu, ctxt->interruptibility); vcpu->arch.emulate_regs_need_sync_to_vcpu = false; kvm_rip_write(vcpu, ctxt->eip); - if (r == EMULATE_DONE && - (ctxt->tf || (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP))) + if (r == EMULATE_DONE && ctxt->tf) kvm_vcpu_do_singlestep(vcpu, &r); if (!ctxt->have_exception || exception_type(ctxt->exception.vector) == EXCPT_TRAP)