From: Gleb Natapov <gleb@kernel.org>
To: tangchen <tangchen@cn.fujitsu.com>
Cc: mtosatti@redhat.com, nadav.amit@gmail.com, jan.kiszka@web.de,
kvm@vger.kernel.org, laijs@cn.fujitsu.com,
isimatu.yasuaki@jp.fujitsu.com, guz.fnst@cn.fujitsu.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 4/6] kvm, mem-hotplug: Reload L1' apic access page on migration in vcpu_enter_guest().
Date: Wed, 3 Sep 2014 18:04:49 +0300 [thread overview]
Message-ID: <20140903150448.GJ18167@minantech.com> (raw)
In-Reply-To: <54067206.7050303@cn.fujitsu.com>
On Wed, Sep 03, 2014 at 09:42:30AM +0800, tangchen wrote:
> Hi Gleb,
>
> On 09/03/2014 12:00 AM, Gleb Natapov wrote:
> >......
> >+static void vcpu_reload_apic_access_page(struct kvm_vcpu *vcpu)
> >+{
> >+ /*
> >+ * apic access page could be migrated. When the page is being migrated,
> >+ * GUP will wait till the migrate entry is replaced with the new pte
> >+ * entry pointing to the new page.
> >+ */
> >+ vcpu->kvm->arch.apic_access_page = gfn_to_page(vcpu->kvm,
> >+ APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT);
> >+ kvm_x86_ops->set_apic_access_page_addr(vcpu->kvm,
> >+ page_to_phys(vcpu->kvm->arch.apic_access_page));
> >I am a little bit worried that here all vcpus write to vcpu->kvm->arch.apic_access_page
> >without any locking. It is probably benign since pointer write is atomic on x86. Paolo?
> >
> >Do we even need apic_access_page? Why not call
> > gfn_to_page(APIC_DEFAULT_PHYS_BASE >> PAGE_SHIFT)
> > put_page()
> >on rare occasions we need to know its address?
>
> Isn't it a necessary item defined in hardware spec ?
>
vcpu->kvm->arch.apic_access_page? No. This is internal kvm data structure.
> I didn't read intel spec deeply, but according to the code, the page's
> address is
> written into vmcs. And it made me think that we cannnot remove it.
>
We cannot remove writing of apic page address into vmcs, but this is not done by
assigning to vcpu->kvm->arch.apic_access_page, but by vmwrite in set_apic_access_page_addr().
--
Gleb.
next prev parent reply other threads:[~2014-09-03 15:05 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-27 10:17 [PATCH v4 0/6] kvm, mem-hotplug: Do not pin ept identity pagetable and apic access page Tang Chen
2014-08-27 10:17 ` [PATCH v4 1/6] kvm: Use APIC_DEFAULT_PHYS_BASE macro as the apic access page address Tang Chen
2014-09-10 13:57 ` Gleb Natapov
2014-08-27 10:17 ` [PATCH v4 2/6] kvm: Remove ept_identity_pagetable from struct kvm_arch Tang Chen
2014-09-10 13:58 ` Gleb Natapov
2014-08-27 10:17 ` [PATCH v4 3/6] kvm: Make init_rmode_identity_map() return 0 on success Tang Chen
2014-08-27 10:17 ` [PATCH v4 4/6] kvm, mem-hotplug: Reload L1' apic access page on migration in vcpu_enter_guest() Tang Chen
2014-09-02 16:00 ` Gleb Natapov
2014-09-03 1:42 ` tangchen
2014-09-03 15:04 ` Gleb Natapov [this message]
2014-09-09 7:13 ` tangchen
2014-09-10 14:01 ` Gleb Natapov
2014-08-27 10:17 ` [PATCH v4 5/6] kvm, mem-hotplug: Reload L1's apic access page on migration when L2 is running Tang Chen
2014-09-03 1:48 ` tangchen
2014-09-03 15:08 ` Gleb Natapov
2014-08-27 10:17 ` [PATCH v4 6/6] kvm, mem-hotplug: Do not pin apic access page in memory Tang Chen
2014-09-01 5:14 ` [PATCH v4 0/6] kvm, mem-hotplug: Do not pin ept identity pagetable and apic access page tangchen
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