linux-kernel - Re: [PATCH v3] kvm/x86: allocate the write-tracking metadata on-demand

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Date: Tue, 27 Feb 2024 13:28:18 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, 
	Andrei Vagin <avagin@...gle.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org, 
	Zhenyu Wang <zhenyuw@...ux.intel.com>, Zhi Wang <zhi.a.wang@...el.com>, 
	Yan Zhao <yan.y.zhao@...el.com>, Yongwei Ma <yongwei.ma@...el.com>
Subject: Re: [PATCH v3] kvm/x86: allocate the write-tracking metadata on-demand

Added a few more KVM-GT folks.  FYI, this changes KVM to allocate metadata for
write-tracking on-demand, i.e. when KVM-GT first registers with KVM.  I tested
by hacking in usage of the external APIs, to register/unregister a node on every
vCPU before/after vcpu_run(), so I am fairly confident that it's functionally
correct.  But just in case you see issues in linux-next... :-)

On Tue, 13 Feb 2024 11:23:40 -0800, Andrei Vagin wrote:
> The write-track is used externally only by the gpu/drm/i915 driver.
> Currently, it is always enabled, if a kernel has been compiled with this
> driver.
> 
> Enabling the write-track mechanism adds a two-byte overhead per page across
> all memory slots. It isn't significant for regular VMs. However in gVisor,
> where the entire process virtual address space is mapped into the VM, even
> with a 39-bit address space, the overhead amounts to 256MB.
> 
> [...]

Applied to kvm-x86 mmu, thanks!

[1/1] kvm/x86: allocate the write-tracking metadata on-demand
      https://github.com/kvm-x86/linux/commit/a364c014a2c1

--
https://github.com/kvm-x86/linux/tree/next