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KVM: x86: do not execute halted vcpus (resend)

DISCUSSION Applied Marcelo Tosatti 2 participants 2 messages Sep 10, 2008 – Sep 11, 2008

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Marcelo Tosatti

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#0 lore raw
Quoted 12 lines · Avi Kivity
Quoted 11 lines · Marcelo Tosatti
Quoted 3 lines

Actually it does reproduce. If you reboot twice, the second reboot will hang during reset (with cs:ip = f000:fff0). Plain Windows XP.

OK, easily reproducible by adding a sleep at the start of qemu_kvm_system_reset.

The problem is that the vcpu HLT's between the KBD ioport write and the actual system reset by the IO thread. By then time there will be no event that takes it out of STATE_HALTED.

Quoted 7 lines
Quoted 4 lines

The following fixes it, however older userspace will remain borked. Alternative is to special case f000:fff0 in-kernel. What is preferred?

Special-case the kvm_set_sregs ioctl with cs:eip f000:fff0 (and cr0.pe=0 for good measure).

KVM: x86: unhalt vcpu0 on reset

Since "KVM: x86: do not execute halted vcpus", HLT by vcpu0 before system reset by the IO thread will hang the guest.

Mark vcpu as runnable in such case.

Signed-off-by Marcelo Tosatti <[email protected]>
arch/x86/kvm/x86.c +5 -0
Index: kvm.tip/arch/x86/kvm/x86.c
===================================================================
@@ -3959,6 +3959,11 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct
 	kvm_set_segment(vcpu, &sregs->tr, VCPU_SREG_TR);
 	kvm_set_segment(vcpu, &sregs->ldt, VCPU_SREG_LDTR);
 
+	if (vcpu->vcpu_id == 0 && kvm_rip_read(vcpu) == 0xfff0 &&
+	    sregs->cs.selector == 0xf000 && sregs->cs.base == 0xffff0000 &&
+	    !(vcpu->arch.cr0 & X86_CR0_PE))
+		vcpu->arch.mp_state = KVM_MP_STATE_RUNNABLE;
+
 	vcpu_put(vcpu);
 
 	return 0;
Applied
#1 lore raw
Quoted 7 lines · Marcelo Tosatti

KVM: x86: unhalt vcpu0 on reset

Since "KVM: x86: do not execute halted vcpus", HLT by vcpu0 before system reset by the IO thread will hang the guest.

Mark vcpu as runnable in such case.

Applied, thanks. I still want userspace fixed, so please resend the libkvm patch, changelogged and signoffed.

Signature · 1 line
Do not meddle in the internals of kernels, for they are subtle and quick to panic.