[PATCH] CPU: abstract read-mostly-ness for per-CPU cpumask_var_t variables

[Jan Beulich <jbeulich@xxxxxxxx>]

cpumask_var_t can resolve to a pointer or to an array. While the pointer
typically is allocated once for a CPU and then only read (i.e. wants to be
marked read-mostly), the same isn't necessarily true for the array case.
There things depend on how the variable is actually used. cpu_core_mask
and cpu_sibling_mask (which all architectures have inherited from x86,
which in turn is possibly wrong) are altered only as CPUs are brought up
or down, so may remain uniformly read-mostly. Other (x86-only) instances
want to change, to avoid disturbing adjacent read-mostly data.

While doing the x86 adjustment, also do one in the opposite direction,
i.e. where there was no read-mostly annotation when it is applicable in
the "pointer" case.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Really in the pointer case it would be nice if the allocations could then
also come from "read-mostly" space.

--- a/xen/arch/x86/genapic/x2apic.c
+++ b/xen/arch/x86/genapic/x2apic.c
@@ -20,7 +20,7 @@
 static DEFINE_PER_CPU_READ_MOSTLY(u32, cpu_2_logical_apicid);
 static DEFINE_PER_CPU_READ_MOSTLY(cpumask_t *, cluster_cpus);
 static cpumask_t *cluster_cpus_spare;
-static DEFINE_PER_CPU(cpumask_var_t, scratch_mask);
+static DEFINE_PER_CPU_CPUMASK_VAR(scratch_mask);
 
 static inline u32 x2apic_cluster(unsigned int cpu)
 {
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -52,13 +52,13 @@ DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t
 /* representing HT and core siblings of each logical CPU */
 DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_core_mask);
 
-DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, scratch_cpumask);
+DEFINE_PER_CPU_CPUMASK_VAR(scratch_cpumask);
 static cpumask_t scratch_cpu0mask;
 
-DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, hpet_scratch_cpumask);
+DEFINE_PER_CPU_CPUMASK_VAR(hpet_scratch_cpumask);
 static cpumask_t hpet_scratch_cpu0mask;
 
-DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, send_ipi_cpumask);
+DEFINE_PER_CPU_CPUMASK_VAR(send_ipi_cpumask);
 static cpumask_t send_ipi_cpu0mask;
 
 DEFINE_PER_CPU_READ_MOSTLY(struct stubs, stubs);
--- a/xen/include/xen/cpumask.h
+++ b/xen/include/xen/cpumask.h
@@ -311,6 +311,9 @@ extern const cpumask_t cpumask_all;
 
 typedef cpumask_t *cpumask_var_t;
 
+#define DEFINE_PER_CPU_CPUMASK_VAR(sym) \
+       DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, sym)
+
 static inline bool alloc_cpumask_var(cpumask_var_t *mask)
 {
        *mask = _xmalloc(nr_cpumask_bits / 8, sizeof(long));
@@ -349,6 +352,9 @@ static inline void free_cpumask_var(cpum
 #else
 typedef cpumask_t cpumask_var_t[1];
 
+#define DEFINE_PER_CPU_CPUMASK_VAR(sym) \
+       DEFINE_PER_CPU(cpumask_var_t, sym)
+
 static inline bool alloc_cpumask_var(cpumask_var_t *mask)
 {
        return true;