This patch adds user eqs exception hooks for async page fault page not present code path, to exit the user eqs and re-enter it as necessary. Async page fault is different from other exceptions that it may be triggered from idle process, so we still need rcu_irq_enter() and rcu_irq_exit() to exit cpu idle eqs when needed, to protect the code that needs use rcu. As Frederic pointed out it would be safest and simplest to protect the whole kvm_async_pf_task_wait(). Otherwise, "we need to check all the code there deeply for potential RCU uses and ensure it will never be extended later to use RCU.". However, We'd better re-enter the cpu idle eqs if we get the exception in cpu idle eqs, by calling rcu_irq_exit() before native_safe_halt(). So the patch does what Frederic suggested for rcu_irq_*() API usage here, except that I moved the rcu_irq_*() pair originally in do_async_page_fault() into kvm_async_pf_task_wait(). That's because, I think it's better to have rcu_irq_*() pairs to be in one function ( rcu_irq_exit() after rcu_irq_enter() ), especially here, kvm_async_pf_task_wait() has other callers, which might cause rcu_irq_exit() be called without a matching rcu_irq_enter() before it, which is illegal if the cpu happens to be in rcu idle state. Signed-off-by: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx> --- arch/x86/kernel/kvm.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 4180a87..342b00b 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -42,6 +42,7 @@ #include <asm/apic.h> #include <asm/apicdef.h> #include <asm/hypervisor.h> +#include <asm/rcu.h> static int kvmapf = 1; @@ -112,6 +113,8 @@ void kvm_async_pf_task_wait(u32 token) DEFINE_WAIT(wait); int cpu, idle; + rcu_irq_enter(); + cpu = get_cpu(); idle = idle_cpu(cpu); put_cpu(); @@ -123,6 +126,8 @@ void kvm_async_pf_task_wait(u32 token) hlist_del(&e->link); kfree(e); spin_unlock(&b->lock); + + rcu_irq_exit(); return; } @@ -147,13 +152,16 @@ void kvm_async_pf_task_wait(u32 token) /* * We cannot reschedule. So halt. */ + rcu_irq_exit(); native_safe_halt(); + rcu_irq_enter(); local_irq_disable(); } } if (!n.halted) finish_wait(&n.wq, &wait); + rcu_irq_exit(); return; } EXPORT_SYMBOL_GPL(kvm_async_pf_task_wait); @@ -247,10 +255,10 @@ do_async_page_fault(struct pt_regs *regs, unsigned long error_code) break; case KVM_PV_REASON_PAGE_NOT_PRESENT: /* page is swapped out by the host. */ - rcu_irq_enter(); + exception_enter(regs); exit_idle(); kvm_async_pf_task_wait((u32)read_cr2()); - rcu_irq_exit(); + exception_exit(regs); break; case KVM_PV_REASON_PAGE_READY: rcu_irq_enter(); -- 1.7.11.4 -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
