linux-kernel - Re: [RFC PATCH] KVM: TDX: Decouple TDX init mem region from kvm_gmem

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Message-ID: <aHoQa4dBSi877f1a@yzhao56-desk.sh.intel.com>
Date: Fri, 18 Jul 2025 17:14:19 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>, Michael Roth
	<michael.roth@....com>, <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <rick.p.edgecombe@...el.com>,
	<kai.huang@...el.com>, <adrian.hunter@...el.com>,
	<reinette.chatre@...el.com>, <xiaoyao.li@...el.com>,
	<tony.lindgren@...el.com>, <binbin.wu@...ux.intel.com>,
	<dmatlack@...gle.com>, <isaku.yamahata@...el.com>, <ira.weiny@...el.com>,
	<vannapurve@...gle.com>, <david@...hat.com>, <ackerleytng@...gle.com>,
	<tabba@...gle.com>, <chao.p.peng@...el.com>
Subject: Re: [RFC PATCH] KVM: TDX: Decouple TDX init mem region from
 kvm_gmem_populate()

On Tue, Jul 15, 2025 at 09:10:42AM +0800, Yan Zhao wrote:
> On Mon, Jul 14, 2025 at 08:46:59AM -0700, Sean Christopherson wrote:
> > > > 	folio = __kvm_gmem_get_pfn(file, slot, index, &pfn, &is_prepared, &max_order);
> > > If max_order > 0 is returned, the next invocation of __kvm_gmem_populate() for
> > > GFN+1 will return is_prepared == true.
> > 
> > I don't see any reason to try and make the current code truly work with hugepages.
> > Unless I've misundertood where we stand, the correctness of hugepage support is
> Hmm. I thought your stand was to address the AB-BA lock issue which will be
> introduced by huge pages, so you moved the get_user_pages() from vendor code to
> the common code in guest_memfd :)
> 
> > going to depend heavily on the implementation for preparedness.  I.e. trying to
> > make this all work with per-folio granulartiy just isn't possible, no?
> Ah. I understand now. You mean the right implementation of __kvm_gmem_get_pfn()
> should return is_prepared at 4KB granularity rather than per-folio granularity.
> 
> So, huge pages still has dependency on the implementation for preparedness.
Looks with [3], is_prepared will not be checked in kvm_gmem_populate().

> Will you post code [1][2] to fix non-hugepages first? Or can I pull them to use
> as prerequisites for TDX huge page v2?
So, maybe I can use [1][2][3] as the base.

> [1] https://lore.kernel.org/all/aG_pLUlHdYIZ2luh@google.com/
> [2] https://lore.kernel.org/all/aHEwT4X0RcfZzHlt@google.com/
[3] https://lore.kernel.org/lkml/20250613005400.3694904-2-michael.roth@amd.com,