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x86/hyperv: check cpu mask after interrupt has been disabled 

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@kernel.org>
Cc: stable@kernel.org
Link: https://lore.kernel.org/r/20210105175043.28325-1-wei.liu@kernel.org
Reviewed-by:  Michael Kelley <mikelley@microsoft.com>
This commit is contained in:
Wei Liu 2021-01-05 17:50:43 +00:00
parent dfe94d4086
commit ad0a6bad44
1 changed files with 9 additions and 3 deletions
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12
arch/x86/hyperv/mmu.c
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@ -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);