linux-kernel - Re: [RFC PATCH 02/12] KVM: x86/mmu: Add dedicated API to map guest

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Message-ID: <4c292519bf58d503c561063d4c139ab918ed3304.camel@intel.com>
Date: Thu, 28 Aug 2025 00:54:48 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>, "Zhao, Yan Y"
	<yan.y.zhao@...el.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "Annapurve, Vishal" <vannapurve@...gle.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"michael.roth@....com" <michael.roth@....com>, "Weiny, Ira"
	<ira.weiny@...el.com>
Subject: Re: [RFC PATCH 02/12] KVM: x86/mmu: Add dedicated API to map
 guest_memfd pfn into TDP MMU

On Wed, 2025-08-27 at 16:25 +0800, Yan Zhao wrote:
> > +{
> > +	struct kvm_page_fault fault = {
> > +		.addr = gfn_to_gpa(gfn),
> > +		.error_code = PFERR_GUEST_FINAL_MASK |
> > PFERR_PRIVATE_ACCESS,
> > +		.prefetch = true,
> > +		.is_tdp = true,
> > +		.nx_huge_page_workaround_enabled =
> > is_nx_huge_page_enabled(vcpu->kvm),
> > +
> > +		.max_level = KVM_MAX_HUGEPAGE_LEVEL,
> Looks the kvm_tdp_mmu_map_private_pfn() is only for initial memory mapping,
> given that ".prefetch = true" and RET_PF_SPURIOUS is not a valid return value.

Hmm, what are you referring to regarding RET_PF_SPURIOUS?

> 
> Then, what about setting
>                 .max_level = PG_LEVEL_4K,
> directly?
> 
> Otherwise, the "(KVM_BUG_ON(level != PG_LEVEL_4K, kvm)" would be triggered in
> tdx_sept_set_private_spte().

Yes this fails to boot a TD. With max_level = PG_LEVEL_4K it passes the full
tests. I don't think it's ideal to encode PAGE.ADD details here though.

But I'm not immediately clear what is going wrong. The old struct kvm_page_fault
looks pretty similar. Did you root cause it?