Re: [PATCH v19 for-4.14 01/13] x86/mem_sharing: block interrupt injection for forks

[Wei Liu <wl@xxxxxxx>]

On Mon, Jun 01, 2020 at 06:21:35AM -0700, Tamas K Lengyel wrote:
> When running VM forks without device models (QEMU), it may
> be undesirable for Xen to inject interrupts. When creating such forks from
> Windows VMs we have observed the kernel trying to process interrupts
> immediately after the fork is executed. However without QEMU running such
> interrupt handling may not be possible because it may attempt to interact with
> devices that are not emulated by a backend. In the best case scenario such
> interrupt handling would only present a detour in the VM forks' execution
> flow, but in the worst case as we actually observed can completely stall it.
> By disabling interrupt injection a fuzzer can exercise the target code without
> interference. For other use-cases this option probably doesn't make sense,
> that's why this is not enabled by default.
> 
> Forks & memory sharing are only available on Intel CPUs so this only applies
> to vmx. Note that this is part of the experimental VM forking feature that's
> completely disabled by default and can only be enabled by using
> XEN_CONFIG_EXPERT during compile time.
> 
> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>
> Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Reviewed-by: Wei Liu <wl@xxxxxxx>