linux-kernel - Re: [PATCH v6 10/12] Handle async PF in non preemptable context

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Message-ID: <20101005195149.GC1786@amt.cnet>
Date:	Tue, 5 Oct 2010 16:51:50 -0300
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	kvm@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, avi@...hat.com, mingo@...e.hu,
	a.p.zijlstra@...llo.nl, tglx@...utronix.de, hpa@...or.com,
	riel@...hat.com, cl@...ux-foundation.org
Subject: Re: [PATCH v6 10/12] Handle async PF in non preemptable context

On Mon, Oct 04, 2010 at 05:56:32PM +0200, Gleb Natapov wrote:
> If async page fault is received by idle task or when preemp_count is
> not zero guest cannot reschedule, so do sti; hlt and wait for page to be
> ready. vcpu can still process interrupts while it waits for the page to
> be ready.
> 
> Acked-by: Rik van Riel <riel@...hat.com>
> Signed-off-by: Gleb Natapov <gleb@...hat.com>
> ---
>  arch/x86/kernel/kvm.c |   40 ++++++++++++++++++++++++++++++++++------
>  1 files changed, 34 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
> index 36fb3e4..f73946f 100644
> --- a/arch/x86/kernel/kvm.c
> +++ b/arch/x86/kernel/kvm.c
> @@ -37,6 +37,7 @@
>  #include <asm/cpu.h>
>  #include <asm/traps.h>
>  #include <asm/desc.h>
> +#include <asm/tlbflush.h>
>  
>  #define MMU_QUEUE_SIZE 1024
>  
> @@ -78,6 +79,8 @@ struct kvm_task_sleep_node {
>  	wait_queue_head_t wq;
>  	u32 token;
>  	int cpu;
> +	bool halted;
> +	struct mm_struct *mm;
>  };
>  
>  static struct kvm_task_sleep_head {
> @@ -106,6 +109,11 @@ void kvm_async_pf_task_wait(u32 token)
>  	struct kvm_task_sleep_head *b = &async_pf_sleepers[key];
>  	struct kvm_task_sleep_node n, *e;
>  	DEFINE_WAIT(wait);
> +	int cpu, idle;
> +
> +	cpu = get_cpu();
> +	idle = idle_cpu(cpu);
> +	put_cpu();
>  
>  	spin_lock(&b->lock);
>  	e = _find_apf_task(b, token);
> @@ -119,19 +127,33 @@ void kvm_async_pf_task_wait(u32 token)
>  
>  	n.token = token;
>  	n.cpu = smp_processor_id();
> +	n.mm = current->active_mm;
> +	n.halted = idle || preempt_count() > 1;
> +	atomic_inc(&n.mm->mm_count);

Can't see why this reference is needed.

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