x86/hyperv: Avoid erroneously sending IPI to 'self'

__send_ipi_mask_ex() uses an optimization: when the target CPU mask is
equal to 'cpu_present_mask' it uses 'HV_GENERIC_SET_ALL' format to avoid
converting the specified cpumask to VP_SET. This case was overlooked when
'exclude_self' parameter was added. As the result, a spurious IPI to
'self' can be send.

Reported-by: Thomas Gleixner <tglx@linutronix.de>
Fixes: dfb5c1e12c28 ("x86/hyperv: remove on-stack cpumask from hv_send_ipi_mask_allbutself")
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20211006125016.941616-1-vkuznets@redhat.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
index 32a1ad356c183f35873cf37926edda5c79c63734..db2d92fb44daf820402f90bd4d320cb5c133477a 100644 (file)
--- a/arch/x86/hyperv/hv_apic.c
+++ b/arch/x86/hyperv/hv_apic.c
@@ -122,17 +122,27 @@ static bool __send_ipi_mask_ex(const struct cpumask *mask, int vector,
        ipi_arg->reserved = 0;
        ipi_arg->vp_set.valid_bank_mask = 0;
 
-       if (!cpumask_equal(mask, cpu_present_mask)) {
+       /*
+        * Use HV_GENERIC_SET_ALL and avoid converting cpumask to VP_SET
+        * when the IPI is sent to all currently present CPUs.
+        */
+       if (!cpumask_equal(mask, cpu_present_mask) || exclude_self) {
                ipi_arg->vp_set.format = HV_GENERIC_SET_SPARSE_4K;
                if (exclude_self)
                        nr_bank = cpumask_to_vpset_noself(&(ipi_arg->vp_set), mask);
                else
                        nr_bank = cpumask_to_vpset(&(ipi_arg->vp_set), mask);
-       }
-       if (nr_bank < 0)
-               goto ipi_mask_ex_done;
-       if (!nr_bank)
+
+               /*
+                * 'nr_bank <= 0' means some CPUs in cpumask can't be
+                * represented in VP_SET. Return an error and fall back to
+                * native (architectural) method of sending IPIs.
+                */
+               if (nr_bank <= 0)
+                       goto ipi_mask_ex_done;
+       } else {
                ipi_arg->vp_set.format = HV_GENERIC_SET_ALL;
+       }
 
        status = hv_do_rep_hypercall(HVCALL_SEND_IPI_EX, 0, nr_bank,
                              ipi_arg, NULL);