linux-kernel - Re: [PATCH 11/18] KVM: MMU: Add infrastructure for two-level page walker

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Message-ID: <20100310144600.GL5619@amd.com>
Date:	Wed, 10 Mar 2010 15:46:00 +0100
From:	Joerg Roedel <joerg.roedel@....com>
To:	Avi Kivity <avi@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Alexander Graf <agraf@...e.de>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 11/18] KVM: MMU: Add infrastructure for two-level page
 walker

On Mon, Mar 08, 2010 at 11:37:22AM +0200, Avi Kivity wrote:
> On 03/03/2010 09:12 PM, Joerg Roedel wrote:
> >This patch introduces a mmu-callback to translate gpa
> >addresses in the walk_addr code. This is later used to
> >translate l2_gpa addresses into l1_gpa addresses.
> >
> >Signed-off-by: Joerg Roedel<joerg.roedel@....com>
> >---
> >  arch/x86/include/asm/kvm_host.h |    1 +
> >  arch/x86/kvm/mmu.c              |    7 +++++++
> >  arch/x86/kvm/paging_tmpl.h      |   19 +++++++++++++++++++
> >  include/linux/kvm_host.h        |    5 +++++
> >  4 files changed, 32 insertions(+), 0 deletions(-)
> >
> >diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> >index c0b5576..76c8b5f 100644
> >--- a/arch/x86/include/asm/kvm_host.h
> >+++ b/arch/x86/include/asm/kvm_host.h
> >@@ -250,6 +250,7 @@ struct kvm_mmu {
> >  	void (*free)(struct kvm_vcpu *vcpu);
> >  	gpa_t (*gva_to_gpa)(struct kvm_vcpu *vcpu, gva_t gva, u32 access,
> >  			    u32 *error);
> >+	gpa_t (*translate_gpa)(struct kvm_vcpu *vcpu, gpa_t gpa, u32 *error);
> >  	void (*prefetch_page)(struct kvm_vcpu *vcpu,
> >  			      struct kvm_mmu_page *page);
> >  	int (*sync_page)(struct kvm_vcpu *vcpu,
> 
> I think placing this here means we will miss a few translations,
> namely when we do a physical access (say, reading PDPTEs or
> similar).
> 
> We need to do this on the level of kvm_read_guest() so we capture
> physical accesses:
> 
> kvm_read_guest_virt
>   -> walk_addr
>      -> kvm_read_guest_tdp
>          -> kvm_read_guest_virt
>             -> walk_addr
>                 -> kvm_read_guest_tdp
>                      -> kvm_read_guest
> 
> Of course, not all accesses will use kvm_read_guest_tdp; for example
> kvmclock accesses should still go untranslated.

Ok, doing the translation in kvm_read_guest is certainly the more
generic approach. I already fixed a bug related to loading l2 pdptr
pointers. Doing the translation in kvm_read_guest makes the code a lot
nicer.

	Joerg


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