[Xen-devel] [PATCH v4 1/2] x86/smp: use a dedicated CPU mask in send_IPI_mask

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Some callers of send_IPI_mask pass the scratch cpumask as the mask
parameter of send_IPI_mask, so the scratch cpumask cannot be used by
the function. The following trace has been obtained with a debug patch
and shows one of those callers:

(XEN) scratch CPU mask already in use by 
arch/x86/mm.c#_get_page_type+0x1f9/0x1abf
(XEN) Xen BUG at smp.c:45
[...]
(XEN) Xen call trace:
(XEN)    [<ffff82d0802abb53>] R scratch_cpumask+0xd3/0xf9
(XEN)    [<ffff82d0802abc21>] F send_IPI_mask+0x72/0x1ca
(XEN)    [<ffff82d0802ac13e>] F flush_area_mask+0x10c/0x16c
(XEN)    [<ffff82d080296c56>] F arch/x86/mm.c#_get_page_type+0x3ff/0x1abf
(XEN)    [<ffff82d080298324>] F get_page_type+0xe/0x2c
(XEN)    [<ffff82d08038624f>] F pv_set_gdt+0xa1/0x2aa
(XEN)    [<ffff82d08027dfd6>] F arch_set_info_guest+0x1196/0x16ba
(XEN)    [<ffff82d080207a55>] F default_initialise_vcpu+0xc7/0xd4
(XEN)    [<ffff82d08027e55b>] F arch_initialise_vcpu+0x61/0xcd
(XEN)    [<ffff82d080207e78>] F do_vcpu_op+0x219/0x690
(XEN)    [<ffff82d08038be16>] F pv_hypercall+0x2f6/0x593
(XEN)    [<ffff82d080396432>] F lstar_enter+0x112/0x120

_get_page_type will use the scratch cpumask to call flush_tlb_mask,
which in turn calls send_IPI_mask.

Fix this by using a dedicated per CPU cpumask in send_IPI_mask.

Fixes: 5500d265a2a8 ('x86/smp: use APIC ALLBUT destination shorthand when 
possible')
Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/smp.c     | 4 +++-
 xen/arch/x86/smpboot.c | 9 ++++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/smp.c b/xen/arch/x86/smp.c
index 0461812cf6..072638f0f6 100644
--- a/xen/arch/x86/smp.c
+++ b/xen/arch/x86/smp.c
@@ -59,6 +59,8 @@ static void send_IPI_shortcut(unsigned int shortcut, int 
vector,
     apic_write(APIC_ICR, cfg);
 }
 
+DECLARE_PER_CPU(cpumask_var_t, send_ipi_cpumask);
+
 /*
  * send_IPI_mask(cpumask, vector): sends @vector IPI to CPUs in @cpumask,
  * excluding the local CPU. @cpumask may be empty.
@@ -67,7 +69,7 @@ static void send_IPI_shortcut(unsigned int shortcut, int 
vector,
 void send_IPI_mask(const cpumask_t *mask, int vector)
 {
     bool cpus_locked = false;
-    cpumask_t *scratch = this_cpu(scratch_cpumask);
+    cpumask_t *scratch = this_cpu(send_ipi_cpumask);
 
     if ( in_irq() || in_mce_handler() || in_nmi_handler() )
     {
diff --git a/xen/arch/x86/smpboot.c b/xen/arch/x86/smpboot.c
index ad49f2dcd7..6c548b0b53 100644
--- a/xen/arch/x86/smpboot.c
+++ b/xen/arch/x86/smpboot.c
@@ -57,6 +57,9 @@ DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_core_mask);
 DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, scratch_cpumask);
 static cpumask_t scratch_cpu0mask;
 
+DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, send_ipi_cpumask);
+static cpumask_t send_ipi_cpu0mask;
+
 cpumask_t cpu_online_map __read_mostly;
 EXPORT_SYMBOL(cpu_online_map);
 
@@ -930,6 +933,8 @@ static void cpu_smpboot_free(unsigned int cpu, bool remove)
         FREE_CPUMASK_VAR(per_cpu(cpu_core_mask, cpu));
         if ( per_cpu(scratch_cpumask, cpu) != &scratch_cpu0mask )
             FREE_CPUMASK_VAR(per_cpu(scratch_cpumask, cpu));
+        if ( per_cpu(send_ipi_cpumask, cpu) != &send_ipi_cpu0mask )
+            FREE_CPUMASK_VAR(per_cpu(send_ipi_cpumask, cpu));
     }
 
     cleanup_cpu_root_pgt(cpu);
@@ -1034,7 +1039,8 @@ static int cpu_smpboot_alloc(unsigned int cpu)
 
     if ( !(cond_zalloc_cpumask_var(&per_cpu(cpu_sibling_mask, cpu)) &&
            cond_zalloc_cpumask_var(&per_cpu(cpu_core_mask, cpu)) &&
-           cond_alloc_cpumask_var(&per_cpu(scratch_cpumask, cpu))) )
+           cond_alloc_cpumask_var(&per_cpu(scratch_cpumask, cpu)) &&
+           cond_alloc_cpumask_var(&per_cpu(send_ipi_cpumask, cpu))) )
         goto out;
 
     rc = 0;
@@ -1175,6 +1181,7 @@ void __init smp_prepare_boot_cpu(void)
     cpumask_set_cpu(cpu, &cpu_present_map);
 #if NR_CPUS > 2 * BITS_PER_LONG
     per_cpu(scratch_cpumask, cpu) = &scratch_cpu0mask;
+    per_cpu(send_ipi_cpumask, cpu) = &send_ipi_cpu0mask;
 #endif
 
     get_cpu_info()->use_pv_cr3 = false;
-- 
2.25.0


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