[PATCH 5.4 04/76] x86/hyperv: check cpu mask after interrupt has been disabled

Greg Kroah-Hartman
2021-01-18T19:20:02Z

From: Wei Liu <wei.liu@kernel.org>

commit ad0a6bad44758afa3b440c254a24999a0c7e35d5 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/hyperv/mmu.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)

--- a/arch/x86/hyperv/mmu.c
+++ b/arch/x86/hyperv/mmu.c
@@ -66,11 +66,17 @@ static void hyperv_flush_tlb_others(cons
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);