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Message-ID: <1354599618.2649.19.camel@ThinkPad-T5421.cn.ibm.com> Date: Tue, 04 Dec 2012 13:40:18 +0800 From: Li Zhong <zhong@...ux.vnet.ibm.com> To: Gleb Natapov <gleb@...hat.com> Cc: Frederic Weisbecker <fweisbec@...il.com>, linux-next list <linux-next@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, paulmck@...ux.vnet.ibm.com, sasha.levin@...cle.com, avi@...hat.com Subject: Re: [RFC PATCH v3] Add rcu user eqs exception hooks for async page fault On Tue, 2012-12-04 at 07:11 +0200, Gleb Natapov wrote: > On Tue, Dec 04, 2012 at 10:36:02AM +0800, Li Zhong wrote: > > On Mon, 2012-12-03 at 11:57 +0200, Gleb Natapov wrote: > > > Please regenerate the patch against > > > git://git.kernel.org/pub/scm/virt/kvm/kvm.git queue. > > > > Done. > > > > By the way, the included file <asm/rcu.h> is replaced with > > <asm/context_tracking.h> in latest next tree(91d1aa43 from rcu tree). > > > What is the url of the rcu tree? git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu.git and the url of the commit: git.kernel.org/?p=linux/kernel/git/paulmck/linux-rcu.git;a=commit;h=91d1aa43d30505b0b825db8898ffc80a8eca96c7 Thanks, Zhong > > > Seems if they are merged, there won't be conflicts, but we need change > > the including file name after that. I don't know how to handle this kind > > of thing... > > > > Thanks, Zhong > > > > > > > > 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@...ux.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 > > > > > > -- > > > Gleb. > > > -- > > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > > > the body of a message to majordomo@...r.kernel.org > > > More majordomo info at http://vger.kernel.org/majordomo-info.html > > > Please read the FAQ at http://www.tux.org/lkml/ > > > > > > > -- > Gleb. > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@...r.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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