KVM: PPC: Book3S HV: Handle unexpected traps in guest entry/exit code better (1c9e3d51) · Commits · 戴 / test

As we saw with the TM Bad Thing type of program interrupt occurring on the hrfid that enters the guest, it is not completely impossible to have a trap occurring in the guest entry/exit code, despite the fact that the code has been written to avoid taking any traps. This adds a check in the kvmppc_handle_exit_hv() function to detect the case when a trap has occurred in the hypervisor-mode code, and instead of treating it just like a trap in guest code, we now print a message and return to userspace with a KVM_EXIT_INTERNAL_ERROR exit reason. Of the various interrupts that get handled in the assembly code in the guest exit path and that can return directly to the guest, the only one that can occur when MSR.HV=1 and MSR.EE=0 is machine check (other than system call, which we can avoid just by not doing a sc instruction). Therefore this adds code to the machine check path to ensure that if the MCE occurred in hypervisor mode, we exit to the host rather than trying to continue the guest. Signed-off-by:

Paul Mackerras <paulus@samba.org>

arch/powerpc/kvm/book3s_hv.c

+18 −0

Original line number	Diff line number	Diff line
		@@ -827,6 +827,24 @@ static int kvmppc_handle_exit_hv(struct kvm_run run, struct kvm_vcpu vcpu,

		vcpu->stat.sum_exits++;

		/*
		* This can happen if an interrupt occurs in the last stages
		* of guest entry or the first stages of guest exit (i.e. after
		* setting paca->kvm_hstate.in_guest to KVM_GUEST_MODE_GUEST_HV
		* and before setting it to KVM_GUEST_MODE_HOST_HV).
		* That can happen due to a bug, or due to a machine check
		* occurring at just the wrong time.
		*/
		if (vcpu->arch.shregs.msr & MSR_HV) {
		printk(KERN_EMERG "KVM trap in HV mode!\n");
		printk(KERN_EMERG "trap=0x%x \| pc=0x%lx \| msr=0x%llx\n",
		vcpu->arch.trap, kvmppc_get_pc(vcpu),
		vcpu->arch.shregs.msr);
		kvmppc_dump_regs(vcpu);
		run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
		run->hw.hardware_exit_reason = vcpu->arch.trap;
		return RESUME_HOST;
		}
		run->exit_reason = KVM_EXIT_UNKNOWN;
		run->ready_for_interrupt_injection = 1;
		switch (vcpu->arch.trap) {

arch/powerpc/kvm/book3s_hv_rmhandlers.S

+2 −0

Original line number	Diff line number	Diff line
		@@ -2404,6 +2404,8 @@ machine_check_realmode:
		* guest as machine check causing guest to crash.
		*/
		ld r11, VCPU_MSR(r9)
		rldicl. r0, r11, 64-MSR_HV_LG, 63 /* check if it happened in HV mode */
		bne mc_cont /* if so, exit to host */
		andi. r10, r11, MSR_RI /* check for unrecoverable exception */
		beq 1f /* Deliver a machine check to guest */
		ld r10, VCPU_PC(r9)

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