[PATCH 4.18 03/22] x86/hyper-v: Check for VP_INVAL in hyperv_flush_tlb_others()

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vitaly Kuznetsov <vkuznets@redhat.com>

commit 110d2a7fc39725d2c29d2fede4f34a35a4f98882 upstream.

Commit 1268ed0c474a ("x86/hyper-v: Fix the circular dependency in IPI
 enlightenment") pre-filled hv_vp_index with VP_INVAL so it is now
(theoretically) possible to observe hv_cpu_number_to_vp_number()
returning VP_INVAL. We need to check for that in hyperv_flush_tlb_others().

Not checking for VP_INVAL on the first call site where we do

 if (hv_cpu_number_to_vp_number(cpumask_last(cpus)) >= 64)
                        goto do_ex_hypercall;

is OK, in case we're eligible for non-ex hypercall we'll catch the
issue later in for_each_cpu() cycle and in case we'll be doing ex-
hypercall cpumask_to_vpset() will fail.

It would be nice to change hv_cpu_number_to_vp_number() return
value's type to 'u32' but this will likely be a bigger change as
all call sites need to be checked first.

Fixes: 1268ed0c474a ("x86/hyper-v: Fix the circular dependency in IPI enlightenment")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Thomas Gleixner <redacted>
Reviewed-by: Michael Kelley <redacted>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <redacted>
Cc: "Michael Kelley (EOSG)" <redacted>
Cc: devel@linuxdriverproject.org
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lkml.kernel.org/r/20180709174012.17429-3-vkuznets@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/x86/hyperv/mmu.c |    5 +++++
 1 file changed, 5 insertions(+)

--- a/arch/x86/hyperv/mmu.c
+++ b/arch/x86/hyperv/mmu.c

@@ -95,6 +95,11 @@ static void hyperv_flush_tlb_others(cons
 	} else {
 		for_each_cpu(cpu, cpus) {
 			vcpu = hv_cpu_number_to_vp_number(cpu);
+			if (vcpu == VP_INVAL) {
+				local_irq_restore(flags);
+				goto do_native;
+			}
+
 			if (vcpu >= 64)
 				goto do_native;