On Fri, Nov 30, 2012 at 05:18:41PM +0800, Li Zhong wrote: > 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(); > + Why move rcu_irq_*() calls into kvm_async_pf_task_wait()? > 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(); We can skip that if rcu_irq_*() will stay outside. > 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 -- Gleb. -- 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
