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

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Message-ID: <aHWqkodwIDZZOtX8@yzhao56-desk>
Date: Tue, 15 Jul 2025 09:10:42 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: 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 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.


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?

[1] https://lore.kernel.org/all/aG_pLUlHdYIZ2luh@google.com/
[2] https://lore.kernel.org/all/aHEwT4X0RcfZzHlt@google.com/

Thanks!