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

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Message-ID: <aN8Vn9iD7OMzspp5@google.com>
Date: Thu, 2 Oct 2025 17:15:27 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Ira Weiny <ira.weiny@...el.com>
Cc: Vishal Annapurve <vannapurve@...gle.com>, Yan Zhao <yan.y.zhao@...el.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, 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 Thu, Oct 02, 2025, Ira Weiny wrote:
> Vishal Annapurve wrote:
> > On Tue, Aug 5, 2025 at 12:59 PM Sean Christopherson <seanjc@...gle.com> wrote:
> > >
> > > On Mon, Aug 04, 2025, Vishal Annapurve wrote:
> > > > On Mon, Aug 4, 2025 at 5:22 PM Sean Christopherson <seanjc@...gle.com> wrote:
> > > > > : 4) For SNP, if src != null, make the target pfn to be shared, copy
> > > > > : contents and then make the target pfn back to private.
> > > > >
> > > > > Copying from userspace under spinlock (rwlock) is illegal, as accessing userspace
> > > > > memory might_fault() and thus might_sleep().
> > > >
> > > > I would think that a combination of get_user_pages() and
> > > > kmap_local_pfn() will prevent this situation of might_fault().
> > >
> > > Yes, but if SNP is using get_user_pages(), then it looks an awful lot like the
> > > TDX flow, at which point isn't that an argument for keeping populate()?
> > 
> > Ack, I agree we can't ditch kvm_gmem_populate() for SNP VMs. I am ok
> > with using it for TDX/CCA VMs with the fixes discussed in this RFC.
> 
> Sean,
> 
> Where did this thread land?  Was there a follow on series which came out
> of this?  I thought you sent a patch with the suggestions in this thread
> but I can't find it.

Are you referring to "KVM: x86/mmu: TDX post-populate cleanups"[*]?  If so, my
goal is to send v3 next week.

If you're talking about something else, then no idea :-)

[*] https://lore.kernel.org/all/20250829000618.351013-1-seanjc@google.com