Re: [PATCH 1/2] KVM: PPC: Book3S HV: Simplify machine check handling

[Mahesh J Salgaonkar <mahesh@linux.vnet.ibm.com>]

On 2019-02-20 12:05:50 Wed, Paul Mackerras wrote:
> This makes the handling of machine check interrupts that occur inside
> a guest simpler and more robust, with less done in assembler code and
> in real mode.
> 
> Now, when a machine check occurs inside a guest, we always get the
> machine check event struct and put a copy in the vcpu struct for the
> vcpu where the machine check occurred.  We no longer call
> machine_check_queue_event() from kvmppc_realmode_mc_power7(), because
> on POWER8, when a vcpu is running on an offline secondary thread and
> we call machine_check_queue_event(), that calls irq_work_queue(),
> which doesn't work because the CPU is offline, but instead triggers
> the WARN_ON(lazy_irq_pending()) in pnv_smp_cpu_kill_self() (which
> fires again and again because nothing clears the condition).
> 
> All that machine_check_queue_event() actually does is to cause the
> event to be printed to the console.  For a machine check occurring in
> the guest, we now print the event in kvmppc_handle_exit_hv()
> instead.
> 
> The assembly code at label machine_check_realmode now just calls C
> code and then continues exiting the guest.  We no longer either
> synthesize a machine check for the guest in assembly code or return
> to the guest without a machine check.
> 
> The code in kvmppc_handle_exit_hv() is extended to handle the case
> where the guest is not FWNMI-capable.  In that case we now always
> synthesize a machine check interrupt for the guest.  Previously, if
> the host thinks it has recovered the machine check fully, it would
> return to the guest without any notification that the machine check
> had occurred.  If the machine check was caused by some action of the
> guest (such as creating duplicate SLB entries), it is much better to
> tell the guest that it has caused a problem.  Therefore we now always
> generate a machine check interrupt for guests that are not
> FWNMI-capable.

Looks good to me.

Reviewed-by: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com>

Thanks,
-Mahesh.