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

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Message-ID: <diqzfrevhmzw.fsf@ackerleytng-ctop.c.googlers.com>
Date: Wed, 16 Jul 2025 13:57:55 -0700
From: Ackerley Tng <ackerleytng@...gle.com>
To: Yan Zhao <yan.y.zhao@...el.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

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
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]).

[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