linux-kernel - Re: [PATCH v15 13/20] KVM: SEV: Implement gmem hook for initializing private pages

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Date: Mon, 20 May 2024 10:35:23 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Kai Huang <kai.huang@...el.com>
Cc: "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>, 
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	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v15 13/20] KVM: SEV: Implement gmem hook for initializing
 private pages

On Mon, May 20, 2024, Kai Huang wrote:
> On Wed, 2024-05-01 at 03:52 -0500, Michael Roth wrote:
> > This will handle the RMP table updates needed to put a page into a
> > private state before mapping it into an SEV-SNP guest.
> > 
> > 
> 
> [...]
> 
> > +int sev_gmem_prepare(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order)

..

> +Rick, Isaku,
> 
> I am wondering whether this can be done in the KVM page fault handler?

No, because the state of a pfn in the RMP is tied to the guest_memfd inode, not
to the file descriptor, i.e. not to an individual VM.  And the NPT page tables
are treated as ephemeral for SNP.