From: Sean Christopherson <seanjc@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: shuah@kernel.org, kvm@vger.kernel.org, catalin.marinas@arm.com,
andrew.jones@linux.dev, dmatlack@google.com,
shan.gavin@gmail.com, bgardon@google.com, kvmarm@lists.linux.dev,
pbonzini@redhat.com, zhenyzha@redhat.com, will@kernel.org,
kvmarm@lists.cs.columbia.edu
Subject: Re: [PATCH v6 3/8] KVM: Add support for using dirty ring in conjunction with bitmap
Date: Thu, 27 Oct 2022 19:09:26 +0000 [thread overview]
Message-ID: <Y1rXZshBbXGjPpTa@google.com> (raw)
In-Reply-To: <875yg5glvk.wl-maz@kernel.org>
On Thu, Oct 27, 2022, Marc Zyngier wrote:
> On Thu, 27 Oct 2022 18:44:51 +0100,
> Sean Christopherson <seanjc@google.com> wrote:
> >
> > On Thu, Oct 27, 2022, Marc Zyngier wrote:
> > > But in the long run, with dirty bits being collected from the IOMMU
> > > page tables or directly from devices, we will need a way to reconcile
> > > the dirty tracking. The above doesn't quite cut it, unfortunately.
> >
> > Oooh, are you referring to IOMMU page tables and devices _in the
> > guest_? E.g. if KVM itself were to emulate a vIOMMU, then KVM would
> > be responsible for updating dirty bits in the vIOMMU page tables.
>
> No. I'm talking about the *physical* IOMMU, which is (with the correct
> architecture revision and feature set) capable of providing its own
> set of dirty bits, on a per-device, per-PTE basis. Once we enable
> that, we'll need to be able to sink these bits into the bitmap and
> provide a unified view of the dirty state to userspace.
Isn't that already handled by VFIO, e.g. via VFIO_IOMMU_DIRTY_PAGES? There may
be "duplicate" information if a page is dirty in both the IOMMU page tables and
the CPU page tables, but that's ok in that the worst case scenario is that the
VMM performs a redundant unnecessary transfer.
A unified dirty bitmap would potentially reduce the memory footprint needed for
dirty logging, but presumably IOMMU-mapped memory is a small subset of CPU-mapped
memory in most use cases.
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WARNING: multiple messages have this Message-ID (diff)
From: Sean Christopherson <seanjc@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>,
Gavin Shan <gshan@redhat.com>,
kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu,
kvm@vger.kernel.org, peterx@redhat.com, will@kernel.org,
catalin.marinas@arm.com, bgardon@google.com, shuah@kernel.org,
andrew.jones@linux.dev, dmatlack@google.com, pbonzini@redhat.com,
zhenyzha@redhat.com, james.morse@arm.com, suzuki.poulose@arm.com,
alexandru.elisei@arm.com, shan.gavin@gmail.com
Subject: Re: [PATCH v6 3/8] KVM: Add support for using dirty ring in conjunction with bitmap
Date: Thu, 27 Oct 2022 19:09:26 +0000 [thread overview]
Message-ID: <Y1rXZshBbXGjPpTa@google.com> (raw)
Message-ID: <20221027190926.nZOm3C6GIX_Gk5LsfZk58iPM5FxZl-EBVaM3llYMq3U@z> (raw)
In-Reply-To: <875yg5glvk.wl-maz@kernel.org>
On Thu, Oct 27, 2022, Marc Zyngier wrote:
> On Thu, 27 Oct 2022 18:44:51 +0100,
> Sean Christopherson <seanjc@google.com> wrote:
> >
> > On Thu, Oct 27, 2022, Marc Zyngier wrote:
> > > But in the long run, with dirty bits being collected from the IOMMU
> > > page tables or directly from devices, we will need a way to reconcile
> > > the dirty tracking. The above doesn't quite cut it, unfortunately.
> >
> > Oooh, are you referring to IOMMU page tables and devices _in the
> > guest_? E.g. if KVM itself were to emulate a vIOMMU, then KVM would
> > be responsible for updating dirty bits in the vIOMMU page tables.
>
> No. I'm talking about the *physical* IOMMU, which is (with the correct
> architecture revision and feature set) capable of providing its own
> set of dirty bits, on a per-device, per-PTE basis. Once we enable
> that, we'll need to be able to sink these bits into the bitmap and
> provide a unified view of the dirty state to userspace.
Isn't that already handled by VFIO, e.g. via VFIO_IOMMU_DIRTY_PAGES? There may
be "duplicate" information if a page is dirty in both the IOMMU page tables and
the CPU page tables, but that's ok in that the worst case scenario is that the
VMM performs a redundant unnecessary transfer.
A unified dirty bitmap would potentially reduce the memory footprint needed for
dirty logging, but presumably IOMMU-mapped memory is a small subset of CPU-mapped
memory in most use cases.
next prev parent reply other threads:[~2022-10-27 19:09 UTC|newest]
Thread overview: 86+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-11 6:14 [PATCH v6 0/8] KVM: arm64: Enable ring-based dirty memory tracking Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 1/8] KVM: x86: Introduce KVM_REQ_RING_SOFT_FULL Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-20 22:42 ` Sean Christopherson
2022-10-20 22:42 ` Sean Christopherson
2022-10-21 5:54 ` Gavin Shan
2022-10-21 5:54 ` Gavin Shan
2022-10-21 15:25 ` Sean Christopherson
2022-10-21 15:25 ` Sean Christopherson
2022-10-21 23:03 ` Gavin Shan
2022-10-21 23:03 ` Gavin Shan
2022-10-21 23:48 ` Sean Christopherson
2022-10-21 23:48 ` Sean Christopherson
2022-10-22 0:16 ` Gavin Shan
2022-10-22 0:16 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 2/8] KVM: x86: Move declaration of kvm_cpu_dirty_log_size() to kvm_dirty_ring.h Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 3/8] KVM: Add support for using dirty ring in conjunction with bitmap Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-18 16:07 ` Peter Xu
2022-10-18 16:07 ` Peter Xu
2022-10-18 22:20 ` Gavin Shan
2022-10-18 22:20 ` Gavin Shan
2022-10-20 18:58 ` Oliver Upton
2022-10-20 18:58 ` Oliver Upton
2022-10-20 23:44 ` Sean Christopherson
2022-10-20 23:44 ` Sean Christopherson
2022-10-21 8:06 ` Marc Zyngier
2022-10-21 8:06 ` Marc Zyngier
2022-10-21 16:05 ` Sean Christopherson
2022-10-21 16:05 ` Sean Christopherson
2022-10-22 8:27 ` Gavin Shan
2022-10-22 8:27 ` Gavin Shan
2022-10-22 10:54 ` Marc Zyngier
2022-10-22 10:54 ` Marc Zyngier
2022-10-22 10:33 ` Marc Zyngier
2022-10-22 10:33 ` Marc Zyngier
2022-10-24 23:50 ` Sean Christopherson
2022-10-24 23:50 ` Sean Christopherson
2022-10-25 0:08 ` Sean Christopherson
2022-10-25 0:08 ` Sean Christopherson
2022-10-25 0:24 ` Oliver Upton
2022-10-25 0:24 ` Oliver Upton
2022-10-25 7:31 ` Marc Zyngier
2022-10-25 7:31 ` Marc Zyngier
2022-10-25 17:47 ` Sean Christopherson
2022-10-25 17:47 ` Sean Christopherson
2022-10-27 8:29 ` Marc Zyngier
2022-10-27 8:29 ` Marc Zyngier
2022-10-27 17:44 ` Sean Christopherson
2022-10-27 17:44 ` Sean Christopherson
2022-10-27 18:30 ` Marc Zyngier
2022-10-27 18:30 ` Marc Zyngier
2022-10-27 19:09 ` Sean Christopherson [this message]
2022-10-27 19:09 ` Sean Christopherson
2022-10-28 6:43 ` Gavin Shan
2022-10-28 6:43 ` Gavin Shan
2022-10-28 16:51 ` Sean Christopherson
2022-10-28 16:51 ` Sean Christopherson
2022-10-31 3:37 ` Gavin Shan
2022-10-31 3:37 ` Gavin Shan
2022-10-31 9:08 ` Marc Zyngier
2022-10-31 9:08 ` Marc Zyngier
2022-10-31 22:48 ` Gavin Shan
2022-10-31 22:48 ` Gavin Shan
2022-10-25 7:22 ` Marc Zyngier
2022-10-25 7:22 ` Marc Zyngier
2022-10-21 10:13 ` Gavin Shan
2022-10-21 10:13 ` Gavin Shan
2022-10-21 23:20 ` Sean Christopherson
2022-10-21 23:20 ` Sean Christopherson
2022-10-22 0:33 ` Gavin Shan
2022-10-22 0:33 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 4/8] KVM: arm64: Enable ring-based dirty memory tracking Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 5/8] KVM: selftests: Enable KVM_CAP_DIRTY_LOG_RING_WITH_BITMAP if possible Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 6/8] KVM: selftests: Use host page size to map ring buffer in dirty_log_test Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 7/8] KVM: selftests: Clear dirty ring states between two modes " Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:14 ` [PATCH v6 8/8] KVM: selftests: Automate choosing dirty ring size " Gavin Shan
2022-10-11 6:14 ` Gavin Shan
2022-10-11 6:23 ` [PATCH v6 0/8] KVM: arm64: Enable ring-based dirty memory tracking Gavin Shan
2022-10-11 6:23 ` Gavin Shan
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