linux-kernel - Re: [PATCH v3 3/3] KVM: MMU: retry #PF for softmmu

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Date:	Wed, 1 Dec 2010 23:19:42 -0200
From:	Marcelo Tosatti <mtosatti@...hat.com>
To:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
Cc:	Avi Kivity <avi@...hat.com>, Gleb Natapov <gleb@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, KVM <kvm@...r.kernel.org>
Subject: Re: [PATCH v3 3/3] KVM: MMU: retry #PF for softmmu

On Tue, Nov 30, 2010 at 05:37:36PM +0800, Xiao Guangrong wrote:
> Retry #PF for softmmu only when the current vcpu has the same root shadow page
> as the time when #PF occurs. it means they have same paging environment
> 
> Signed-off-by: Xiao Guangrong <xiaoguangrong@...fujitsu.com>
> ---
>  arch/x86/include/asm/kvm_host.h |    5 +++++
>  arch/x86/kvm/mmu.c              |   33 ++++++++++++++++++++++++++++++++-
>  arch/x86/kvm/paging_tmpl.h      |   34 +++++++++++++++++++++++-----------
>  arch/x86/kvm/x86.c              |   13 ++++++++++++-
>  virt/kvm/async_pf.c             |    1 +
>  5 files changed, 73 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 209da89..5acbcab 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -191,6 +191,7 @@ union kvm_mmu_page_role {
>  struct kvm_mmu_page {
>  	struct list_head link;
>  	struct hlist_node hash_link;
> +	struct kref apfs_counter;
>  
>  	/*
>  	 * The following two entries are used to key the shadow page in the
> @@ -602,6 +603,7 @@ struct kvm_x86_ops {
>  struct kvm_arch_async_pf {
>  	u32 token;
>  	gfn_t gfn;
> +	struct kvm_mmu_page *root_sp;
>  	bool direct_map;
>  };

Can't you just compare cr3 value? Its harmless to instantiate an spte
for an unused translation.


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