[xen stable-4.13] xen: fix for_each_cpu when NR_CPUS=1

[patchbot@xxxxxxx]

commit 520d3b804f52147073f2ca890e6f588f39396990
Author:     Dario Faggioli <dfaggioli@xxxxxxxx>
AuthorDate: Thu Mar 18 15:07:17 2021 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Mar 18 15:07:17 2021 +0100

    xen: fix for_each_cpu when NR_CPUS=1
    
    When running an hypervisor build with NR_CPUS=1 for_each_cpu does not
    take into account whether the bit of the CPU is set or not in the
    provided mask.
    
    This means that whatever we have in the bodies of these loops is always
    done once, even if the mask was empty and it should never be done. This
    is clearly a bug and was in fact causing an assert to trigger in credit2
    code.
    
    Removing the special casing of NR_CPUS == 1 makes things work again.
    
    Reported-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Signed-off-by: Dario Faggioli <dfaggioli@xxxxxxxx>
    Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: aa50f45332f17e8d6308b996d890d3e83748a1a5
    master date: 2021-03-12 17:02:47 +0100
---
 xen/include/xen/cpumask.h | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/xen/include/xen/cpumask.h b/xen/include/xen/cpumask.h
index 256b60b106..e69589fc08 100644
--- a/xen/include/xen/cpumask.h
+++ b/xen/include/xen/cpumask.h
@@ -368,15 +368,10 @@ static inline void free_cpumask_var(cpumask_var_t mask)
 #define FREE_CPUMASK_VAR(m) free_cpumask_var(m)
 #endif
 
-#if NR_CPUS > 1
 #define for_each_cpu(cpu, mask)                        \
        for ((cpu) = cpumask_first(mask);       \
             (cpu) < nr_cpu_ids;                \
             (cpu) = cpumask_next(cpu, mask))
-#else /* NR_CPUS == 1 */
-#define for_each_cpu(cpu, mask)                        \
-       for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)(mask))
-#endif /* NR_CPUS */
 
 /*
  * The following particular system cpumasks and operations manage
--
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