linux-kernel - Re: [RFC PATCH 08/21] KVM: TDX: Increase/decrease folio ref for huge pages

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Message-ID: <aHnghFAH5N7eiCXo@yzhao56-desk.sh.intel.com>
Date: Fri, 18 Jul 2025 13:49:56 +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>,
	<linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>, <x86@...nel.org>,
	<rick.p.edgecombe@...el.com>, <dave.hansen@...el.com>,
	<kirill.shutemov@...el.com>, <tabba@...gle.com>, <quic_eberman@...cinc.com>,
	<michael.roth@....com>, <david@...hat.com>, <vbabka@...e.cz>,
	<jroedel@...e.de>, <thomas.lendacky@....com>, <pgonda@...gle.com>,
	<zhiquan1.li@...el.com>, <fan.du@...el.com>, <jun.miao@...el.com>,
	<ira.weiny@...el.com>, <isaku.yamahata@...el.com>, <xiaoyao.li@...el.com>,
	<binbin.wu@...ux.intel.com>, <chao.p.peng@...el.com>
Subject: Re: [RFC PATCH 08/21] KVM: TDX: Increase/decrease folio ref for huge
 pages

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.


> [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