From: harry harry <hiharryharryharry@gmail.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Maxim Levitsky <mlevitsk@redhat.com>,
qemu-devel@nongnu.org, mathieu.tarral@protonmail.com,
stefanha@redhat.com, libvir-list@redhat.com, kvm@vger.kernel.org,
pbonzini@redhat.com
Subject: Re: Why guest physical addresses are not the same as the corresponding host virtual addresses in QEMU/KVM? Thanks!
Date: Tue, 13 Oct 2020 01:00:47 -0400 [thread overview]
Message-ID: <CA+-xGqNd37hyhAbkWxcze3YoVxY3a=_79b+ecF9+ZFCpbqcnnA@mail.gmail.com> (raw)
In-Reply-To: <20201012165428.GD26135@linux.intel.com>
BTW, I still have one more question as follows. Thanks!
On Mon, Oct 12, 2020 at 12:54 PM Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
>
> No, the guest physical address spaces is not intrinsically tied to the host
> virtual address spaces. The fact that GPAs and HVAs are related in KVM is a
> property KVM's architecture. EPT/NPT has absolutely nothing to do with HVAs.
>
> As Maxim pointed out, KVM links a guest's physical address space, i.e. GPAs, to
> the host's virtual address space, i.e. HVAs, via memslots. For all intents and
> purposes, this is an extra layer of address translation that is purely software
> defined. The memslots allow KVM to retrieve the HPA for a given GPA when
> servicing a shadow page fault (a.k.a. EPT violation).
>
> When EPT is enabled, a shadow page fault due to an unmapped GPA will look like:
>
> GVA -> [guest page tables] -> GPA -> EPT Violation VM-Exit
>
> The above walk of the guest page tables is done in hardware. KVM then does the
> following walks in software to retrieve the desired HPA:
>
> GPA -> [memslots] -> HVA -> [host page tables] -> HPA
>
> KVM then takes the resulting HPA and shoves it into KVM's shadow page tables,
> or when TDP is enabled, the EPT/NPT page tables. When the guest is run with
> TDP enabled, GVA->HPA translations look like the following, with all walks done
> in hardware.
>
> GVA -> [guest page tables] -> GPA -> [extended/nested page tables] -> HPA
If I understand correctly, the hardware logic of MMU to walk ``GPA ->
[extended/nested page tables] -> HPA''[1] should be the same as ``HVA
-> [host page tables] -> HPA"[2]. If not true, how does KVM find the
correct HPAs when there are EPT violations?
[1] Please note that this hardware walk is the last step, which only
translates the guest physical address to the host physical address
through the four-level nested page table.
[2] Please note that this hardware walk assumes translating the HVA to
the HPA without virtualization involvement.
Thanks,
Harry
WARNING: multiple messages have this Message-ID (diff)
From: harry harry <hiharryharryharry@gmail.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: kvm@vger.kernel.org, libvir-list@redhat.com,
qemu-devel@nongnu.org, Maxim Levitsky <mlevitsk@redhat.com>,
mathieu.tarral@protonmail.com, stefanha@redhat.com,
pbonzini@redhat.com
Subject: Re: Why guest physical addresses are not the same as the corresponding host virtual addresses in QEMU/KVM? Thanks!
Date: Tue, 13 Oct 2020 01:00:47 -0400 [thread overview]
Message-ID: <CA+-xGqNd37hyhAbkWxcze3YoVxY3a=_79b+ecF9+ZFCpbqcnnA@mail.gmail.com> (raw)
In-Reply-To: <20201012165428.GD26135@linux.intel.com>
BTW, I still have one more question as follows. Thanks!
On Mon, Oct 12, 2020 at 12:54 PM Sean Christopherson
<sean.j.christopherson@intel.com> wrote:
>
> No, the guest physical address spaces is not intrinsically tied to the host
> virtual address spaces. The fact that GPAs and HVAs are related in KVM is a
> property KVM's architecture. EPT/NPT has absolutely nothing to do with HVAs.
>
> As Maxim pointed out, KVM links a guest's physical address space, i.e. GPAs, to
> the host's virtual address space, i.e. HVAs, via memslots. For all intents and
> purposes, this is an extra layer of address translation that is purely software
> defined. The memslots allow KVM to retrieve the HPA for a given GPA when
> servicing a shadow page fault (a.k.a. EPT violation).
>
> When EPT is enabled, a shadow page fault due to an unmapped GPA will look like:
>
> GVA -> [guest page tables] -> GPA -> EPT Violation VM-Exit
>
> The above walk of the guest page tables is done in hardware. KVM then does the
> following walks in software to retrieve the desired HPA:
>
> GPA -> [memslots] -> HVA -> [host page tables] -> HPA
>
> KVM then takes the resulting HPA and shoves it into KVM's shadow page tables,
> or when TDP is enabled, the EPT/NPT page tables. When the guest is run with
> TDP enabled, GVA->HPA translations look like the following, with all walks done
> in hardware.
>
> GVA -> [guest page tables] -> GPA -> [extended/nested page tables] -> HPA
If I understand correctly, the hardware logic of MMU to walk ``GPA ->
[extended/nested page tables] -> HPA''[1] should be the same as ``HVA
-> [host page tables] -> HPA"[2]. If not true, how does KVM find the
correct HPAs when there are EPT violations?
[1] Please note that this hardware walk is the last step, which only
translates the guest physical address to the host physical address
through the four-level nested page table.
[2] Please note that this hardware walk assumes translating the HVA to
the HPA without virtualization involvement.
Thanks,
Harry
next prev parent reply other threads:[~2020-10-13 5:01 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-11 5:26 Why guest physical addresses are not the same as the corresponding host virtual addresses in QEMU/KVM? Thanks! harry harry
2020-10-11 5:26 ` harry harry
2020-10-11 7:29 ` Maxim Levitsky
2020-10-11 7:29 ` Maxim Levitsky
2020-10-11 14:11 ` harry harry
2020-10-11 14:11 ` harry harry
2020-10-12 16:54 ` Sean Christopherson
2020-10-12 16:54 ` Sean Christopherson
2020-10-13 4:30 ` harry harry
2020-10-13 4:30 ` harry harry
2020-10-13 4:52 ` Sean Christopherson
2020-10-13 4:52 ` Sean Christopherson
2020-10-13 5:33 ` harry harry
2020-10-13 5:46 ` harry harry
2020-10-13 6:43 ` Paolo Bonzini
2020-10-13 6:43 ` Paolo Bonzini
2020-10-13 20:36 ` harry harry
2020-10-13 20:36 ` harry harry
2020-10-14 8:27 ` Paolo Bonzini
2020-10-14 8:27 ` Paolo Bonzini
2020-10-14 8:29 ` Maxim Levitsky
2020-10-14 8:29 ` Maxim Levitsky
2020-10-15 3:45 ` harry harry
2020-10-15 3:45 ` harry harry
2020-10-13 7:03 ` Sean Christopherson
2020-10-13 7:03 ` Sean Christopherson
2020-10-13 22:40 ` harry harry
2020-10-13 22:40 ` harry harry
2020-10-14 8:28 ` Paolo Bonzini
2020-10-14 8:28 ` Paolo Bonzini
2020-10-15 3:43 ` harry harry
2020-10-15 3:43 ` harry harry
2020-10-13 5:00 ` harry harry [this message]
2020-10-13 5:00 ` harry harry
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