diff options
| -rw-r--r-- | arch/powerpc/include/asm/paravirt.h | 22 |
1 files changed, 18 insertions, 4 deletions
diff --git a/arch/powerpc/include/asm/paravirt.h b/arch/powerpc/include/asm/paravirt.h index bcb7b5f917be..39f173961f6a 100644 --- a/arch/powerpc/include/asm/paravirt.h +++ b/arch/powerpc/include/asm/paravirt.h @@ -21,7 +21,7 @@ static inline bool is_shared_processor(void) return static_branch_unlikely(&shared_processor); } -/* If bit 0 is set, the cpu has been preempted */ +/* If bit 0 is set, the cpu has been ceded, conferred, or preempted */ static inline u32 yield_count_of(int cpu) { __be32 yield_count = READ_ONCE(lppaca_of(cpu).yield_count); @@ -92,6 +92,19 @@ static inline void prod_cpu(int cpu) #define vcpu_is_preempted vcpu_is_preempted static inline bool vcpu_is_preempted(int cpu) { + /* + * The dispatch/yield bit alone is an imperfect indicator of + * whether the hypervisor has dispatched @cpu to run on a physical + * processor. When it is clear, @cpu is definitely not preempted. + * But when it is set, it means only that it *might* be, subject to + * other conditions. So we check other properties of the VM and + * @cpu first, resorting to the yield count last. + */ + + /* + * Hypervisor preemption isn't possible in dedicated processor + * mode by definition. + */ if (!is_shared_processor()) return false; @@ -100,9 +113,10 @@ static inline bool vcpu_is_preempted(int cpu) int first_cpu = cpu_first_thread_sibling(smp_processor_id()); /* - * Preemption can only happen at core granularity. This CPU - * is not preempted if one of the CPU of this core is not - * preempted. + * The PowerVM hypervisor dispatches VMs on a whole core + * basis. So we know that a thread sibling of the local CPU + * cannot have been preempted by the hypervisor, even if it + * has called H_CONFER, which will set the yield bit. */ if (cpu_first_thread_sibling(cpu) == first_cpu) return false; |