From: Li Zhong <zhong@linux•vnet.ibm.com>
To: Frederic Weisbecker <fweisbec@gmail•com>
Cc: Gleb Natapov <gleb@redhat•com>,
linux-next list <linux-next@vger•kernel.org>,
LKML <linux-kernel@vger•kernel.org>,
paulmck@linux•vnet.ibm.com, sasha.levin@oracle•com,
avi@redhat•com
Subject: [RFC PATCH v3] Add rcu user eqs exception hooks for async page fault
Date: Fri, 30 Nov 2012 17:18:41 +0800 [thread overview]
Message-ID: <1354267121.2552.65.camel@ThinkPad-T5421.cn.ibm.com> (raw)
In-Reply-To: <CAFTL4hyHW3uJHvzxz1o4agtGbicFAP1DuUsifbOrp1Q3ODRBMA@mail.gmail.com>
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@linux•vnet.ibm.com>
---
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
next prev parent reply other threads:[~2012-11-30 9:18 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-27 5:15 [RFC PATCH] Fix abnormal rcu dynticks_nesting values related to async page fault Li Zhong
2012-11-27 5:58 ` [PATCH rcu] use new nesting value for rcu_dyntick trace in rcu_eqs_enter_common Li Zhong
2012-11-27 15:18 ` Paul E. McKenney
2012-11-27 13:07 ` [RFC PATCH] Fix abnormal rcu dynticks_nesting values related to async page fault Gleb Natapov
2012-11-27 14:01 ` Sasha Levin
2012-11-27 15:25 ` Paul E. McKenney
2012-11-27 15:34 ` Frederic Weisbecker
2012-11-27 14:38 ` Frederic Weisbecker
2012-11-27 15:44 ` Gleb Natapov
2012-11-27 15:56 ` Frederic Weisbecker
2012-11-27 16:19 ` Paul E. McKenney
2012-11-27 16:48 ` Frederic Weisbecker
2012-11-27 16:59 ` Paul E. McKenney
2012-11-27 16:39 ` Gleb Natapov
2012-11-27 16:51 ` Frederic Weisbecker
2012-11-27 17:00 ` Gleb Natapov
2012-11-27 17:30 ` Frederic Weisbecker
2012-11-27 17:47 ` Gleb Natapov
2012-11-27 18:12 ` Frederic Weisbecker
2012-11-27 19:27 ` Gleb Natapov
2012-11-27 22:53 ` Frederic Weisbecker
2012-11-27 22:54 ` Frederic Weisbecker
2012-11-27 15:39 ` Frederic Weisbecker
2012-11-27 16:16 ` Paul E. McKenney
2012-11-27 16:31 ` Frederic Weisbecker
2012-11-27 16:29 ` Frederic Weisbecker
2012-11-28 8:18 ` [RFC PATCH v2] Add rcu user eqs exception hooks for " Li Zhong
2012-11-28 12:55 ` Frederic Weisbecker
2012-11-28 13:53 ` Gleb Natapov
2012-11-28 14:25 ` Frederic Weisbecker
2012-11-29 11:07 ` Gleb Natapov
2012-11-29 14:47 ` Frederic Weisbecker
2012-11-30 9:18 ` Li Zhong [this message]
2012-11-30 10:26 ` [RFC PATCH v3] " Gleb Natapov
2012-12-03 2:08 ` Li Zhong
2012-12-03 8:30 ` Gleb Natapov
2012-12-03 9:57 ` Gleb Natapov
2012-12-04 2:35 ` [ PATCH] " Li Zhong
2012-12-18 13:25 ` Gleb Natapov
2012-12-04 2:36 ` [RFC PATCH v3] " Li Zhong
2012-12-04 5:11 ` Gleb Natapov
2012-12-04 5:40 ` Li Zhong
2012-12-04 13:02 ` Gleb Natapov
2012-12-04 14:28 ` Paul E. McKenney
2012-11-29 1:49 ` [RFC PATCH v2] " Li Zhong
2012-11-29 14:40 ` Frederic Weisbecker
2012-11-29 17:25 ` Gleb Natapov
2012-11-30 8:36 ` Li Zhong
2012-11-30 10:08 ` Gleb Natapov
2012-11-27 16:43 ` [RFC PATCH] Fix abnormal rcu dynticks_nesting values related to " Frederic Weisbecker
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