From: Wei Liu <wei.liu@xxxxxxxxxx> Sent: Tuesday, January 5, 2021 9:51 AM
>
> We've observed crashes due to an empty cpu mask in
> hyperv_flush_tlb_others. Obviously the cpu mask in question is changed
> between the cpumask_empty call at the beginning of the function and when
> it is actually used later.
>
> One theory is that an interrupt comes in between and a code path ends up
> changing the mask. Move the check after interrupt has been disabled to
> see if it fixes the issue.
>
> Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxx
> ---
> arch/x86/hyperv/mmu.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/hyperv/mmu.c b/arch/x86/hyperv/mmu.c
> index 5208ba49c89a..2c87350c1fb0 100644
> --- a/arch/x86/hyperv/mmu.c
> +++ b/arch/x86/hyperv/mmu.c
> @@ -66,11 +66,17 @@ static void hyperv_flush_tlb_others(const struct cpumask *cpus,
> if (!hv_hypercall_pg)
> goto do_native;
>
> - if (cpumask_empty(cpus))
> - return;
> -
> local_irq_save(flags);
>
> + /*
> + * Only check the mask _after_ interrupt has been disabled to avoid the
> + * mask changing under our feet.
> + */
> + if (cpumask_empty(cpus)) {
> + local_irq_restore(flags);
> + return;
> + }
> +
> flush_pcpu = (struct hv_tlb_flush **)
> this_cpu_ptr(hyperv_pcpu_input_arg);
>
> --
> 2.20.1
Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
