80 lines
2.8 KiB
Diff
80 lines
2.8 KiB
Diff
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References: bsc#1214718
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# Commit 171c52fba5d94e050d704770480dcb983490d0ad
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# Date 2024-06-12 14:29:31 +0200
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# Author Roger Pau Monné <roger.pau@citrix.com>
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# Committer Jan Beulich <jbeulich@suse.com>
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x86/smp: do not use shorthand IPI destinations in CPU hot{,un}plug contexts
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Due to the current rwlock logic, if the CPU calling get_cpu_maps() does
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so from a cpu_hotplug_{begin,done}() region the function will still
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return success, because a CPU taking the rwlock in read mode after
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having taken it in write mode is allowed. Such corner case makes using
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get_cpu_maps() alone not enough to prevent using the shorthand in CPU
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hotplug regions.
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Introduce a new helper to detect whether the current caller is between a
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cpu_hotplug_{begin,done}() region and use it in send_IPI_mask() to restrict
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shorthand usage.
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Fixes: 5500d265a2a8 ('x86/smp: use APIC ALLBUT destination shorthand when possible')
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Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
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Reviewed-by: Jan Beulich <jbeulich@suse.com>
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--- a/xen/arch/x86/smp.c
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+++ b/xen/arch/x86/smp.c
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@@ -88,7 +88,7 @@ void send_IPI_mask(const cpumask_t *mask
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* the system have been accounted for.
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*/
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if ( system_state > SYS_STATE_smp_boot &&
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- !unaccounted_cpus && !disabled_cpus &&
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+ !unaccounted_cpus && !disabled_cpus && !cpu_in_hotplug_context() &&
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/* NB: get_cpu_maps lock requires enabled interrupts. */
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local_irq_is_enabled() && (cpus_locked = get_cpu_maps()) &&
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(park_offline_cpus ||
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--- a/xen/common/cpu.c
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+++ b/xen/common/cpu.c
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@@ -68,6 +68,11 @@ void cpu_hotplug_done(void)
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write_unlock(&cpu_add_remove_lock);
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}
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+bool cpu_in_hotplug_context(void)
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+{
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+ return rw_is_write_locked_by_me(&cpu_add_remove_lock);
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+}
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+
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static NOTIFIER_HEAD(cpu_chain);
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void __init register_cpu_notifier(struct notifier_block *nb)
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--- a/xen/include/xen/cpu.h
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+++ b/xen/include/xen/cpu.h
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@@ -13,6 +13,16 @@ void put_cpu_maps(void);
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void cpu_hotplug_begin(void);
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void cpu_hotplug_done(void);
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+/*
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+ * Returns true when the caller CPU is between a cpu_hotplug_{begin,done}()
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+ * region.
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+ *
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+ * This is required to safely identify hotplug contexts, as get_cpu_maps()
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+ * would otherwise succeed because a caller holding the lock in write mode is
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+ * allowed to acquire the same lock in read mode.
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+ */
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+bool cpu_in_hotplug_context(void);
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+
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/* Receive notification of CPU hotplug events. */
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void register_cpu_notifier(struct notifier_block *nb);
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--- a/xen/include/xen/rwlock.h
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+++ b/xen/include/xen/rwlock.h
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@@ -309,6 +309,8 @@ static always_inline void write_lock_irq
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#define rw_is_locked(l) _rw_is_locked(l)
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#define rw_is_write_locked(l) _rw_is_write_locked(l)
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+#define rw_is_write_locked_by_me(l) \
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+ lock_evaluate_nospec(_is_write_locked_by_me(atomic_read(&(l)->cnts)))
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typedef struct percpu_rwlock percpu_rwlock_t;
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