Message-ID: <aH8xkkArWBrjzYfk@yzhao56-desk.sh.intel.com>
Date: Tue, 22 Jul 2025 14:37:06 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Ackerley Tng <ackerleytng@...gle.com>
CC: <vannapurve@...gle.com>, <pbonzini@...hat.com>, <seanjc@...gle.com>,
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Subject: Re: [RFC PATCH 08/21] KVM: TDX: Increase/decrease folio ref for huge
 pages

On Mon, Jul 21, 2025 at 10:33:14PM -0700, Ackerley Tng wrote:
> Yan Zhao <yan.y.zhao@...el.com> writes:
> 
> > On Wed, Jul 16, 2025 at 01:57:55PM -0700, Ackerley Tng wrote:
> >> Yan Zhao <yan.y.zhao@...el.com> writes:
> >> 
> >> > On Thu, Jun 05, 2025 at 03:35:50PM -0700, Ackerley Tng wrote:
> >> >> Yan Zhao <yan.y.zhao@...el.com> writes:
> >> >> 
> >> >> > On Wed, Jun 04, 2025 at 01:02:54PM -0700, Ackerley Tng wrote:
> >> >> >> Hi Yan,
> >> >> >> 
> >> >> >> While working on the 1G (aka HugeTLB) page support for guest_memfd
> >> >> >> series [1], we took into account conversion failures too. The steps are
> >> >> >> in kvm_gmem_convert_range(). (It might be easier to pull the entire
> >> >> >> series from GitHub [2] because the steps for conversion changed in two
> >> >> >> separate patches.)
> >> >> > ...
> >> >> >> [2] https://github.com/googleprodkernel/linux-cc/tree/gmem-1g-page-support-rfc-v2
> >> >> >
> >> >> > Hi Ackerley,
> >> >> > Thanks for providing this branch.
> >> >> 
> >> >> Here's the WIP branch [1], which I initially wasn't intending to make
> >> >> super public since it's not even RFC standard yet and I didn't want to
> >> >> add to the many guest_memfd in-flight series, but since you referred to
> >> >> it, [2] is a v2 of the WIP branch :)
> >> >> 
> >> >> [1] https://github.com/googleprodkernel/linux-cc/commits/wip-tdx-gmem-conversions-hugetlb-2mept
> >> >> [2] https://github.com/googleprodkernel/linux-cc/commits/wip-tdx-gmem-conversions-hugetlb-2mept-v2
> >> > Hi Ackerley,
> >> >
> >> > I'm working on preparing TDX huge page v2 based on [2] from you. The current
> >> > decision is that the code base of TDX huge page v2 needs to include DPAMT
> >> > and VM shutdown optimization as well.
> >> >
> >> > So, we think kvm-x86/next is a good candidate for us.
> >> > (It is in repo https://github.com/kvm-x86/linux.git
> >> >  commit 87198fb0208a (tag: kvm-x86-next-2025.07.15, kvm-x86/next) Merge branch 'vmx',
> >> >  which already includes code for VM shutdown optimization).
> >> > I still need to port DPAMT + gmem 1G + TDX huge page v2 on top it.
> >> >
> >> > Therefore, I'm wondering if the rebase of [2] onto kvm-x86/next can be done
> >> > from your side. A straightforward rebase is sufficient, with no need for
> >> > any code modification. And it's better to be completed by the end of next
> >> > week.
> >> >
> >> > We thought it might be easier for you to do that (but depending on your
> >> > bandwidth), allowing me to work on the DPAMT part for TDX huge page v2 in
> >> > parallel.
> >> >
> >> 
> >> I'm a little tied up with some internal work, is it okay if, for the
> > No problem.
> >
> >> next RFC, you base the changes that you need to make for TDX huge page
> >> v2 and DPAMT on the base of [2]?
> >
> >> That will save both of us the rebasing. [2] was also based on (some
> >> other version of) kvm/next.
> >> 
> >> I think it's okay since the main goal is to show that it works. I'll
> >> let you know when I can get to a guest_memfd_HugeTLB v3 (and all the
> >> other patches that go into [2]).
> > Hmm, the upstream practice is to post code based on latest version, and
> > there're lots TDX relates fixes in latest kvm-x86/next.
> >
> 
> Yup I understand.
> 
> For guest_memfd//HugeTLB I'm still waiting for guest_memfd//mmap
> (managed by Fuad) to settle, and there are plenty of comments for the
> guest_memfd//conversion component to iron out still, so the full update
> to v3 will take longer than I think you want to wait.
> 
> I'd say for RFCs it's okay to post patch series based on some snapshot,
> since there are so many series in flight?
> 
> To unblock you, if posting based on a snapshot is really not okay, here
> are some other options I can think of:
> 
> a. Use [2] and posting a link to a WIP tree, similar to how [2] was
>    done
> b. Use some placeholder patches, assuming some interfaces to
>    guest_memfd//HugeTLB, like how the first few patches in this series
>    assumes some interfaces of guest_memfd with THP support, and post a
>    series based on assumed interfaces
> 
> Please let me know if one of those options allow you to proceed, thanks!
Do you see any issues with directly rebasing [2] onto 6.16.0-rc6?

We currently prefer this approach. We have tested [2] for some time, and TDX
huge page series doesn't rely on the implementation details of guest_memfd.

It's ok if you are currently occupied by Google's internal tasks. No worries.

> >> [2] https://github.com/googleprodkernel/linux-cc/commits/wip-tdx-gmem-conversions-hugetlb-2mept-v2
> >> 
> >> > However, if it's difficult for you, please feel free to let us know.
> >> >
> >> > Thanks
> >> > Yan

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