linux-kernel - Re: [PATCH v3 04/25] KVM: x86/mmu: Add dedicated API to map guest

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Message-ID: <aPnP07JAYdJurxKo@yzhao56-desk.sh.intel.com>
Date: Thu, 23 Oct 2025 14:48:51 +0800
From: Yan Zhao <yan.y.zhao@...el.com>
To: Sean Christopherson <seanjc@...gle.com>
CC: Marc Zyngier <maz@...nel.org>, Oliver Upton <oliver.upton@...ux.dev>,
	Tianrui Zhao <zhaotianrui@...ngson.cn>, Bibo Mao <maobibo@...ngson.cn>,
	Huacai Chen <chenhuacai@...nel.org>, Madhavan Srinivasan
	<maddy@...ux.ibm.com>, Anup Patel <anup@...infault.org>, Paul Walmsley
	<pjw@...nel.org>, Palmer Dabbelt <palmer@...belt.com>, Albert Ou
	<aou@...s.berkeley.edu>, Christian Borntraeger <borntraeger@...ux.ibm.com>,
	Janosch Frank <frankja@...ux.ibm.com>, Claudio Imbrenda
	<imbrenda@...ux.ibm.com>, Paolo Bonzini <pbonzini@...hat.com>, "Kirill A.
 Shutemov" <kas@...nel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<kvmarm@...ts.linux.dev>, <kvm@...r.kernel.org>, <loongarch@...ts.linux.dev>,
	<linux-mips@...r.kernel.org>, <linuxppc-dev@...ts.ozlabs.org>,
	<kvm-riscv@...ts.infradead.org>, <linux-riscv@...ts.infradead.org>,
	<x86@...nel.org>, <linux-coco@...ts.linux.dev>,
	<linux-kernel@...r.kernel.org>, Ira Weiny <ira.weiny@...el.com>, Kai Huang
	<kai.huang@...el.com>, Michael Roth <michael.roth@....com>, Vishal Annapurve
	<vannapurve@...gle.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Ackerley Tng <ackerleytng@...gle.com>, Binbin Wu <binbin.wu@...ux.intel.com>
Subject: Re: [PATCH v3 04/25] KVM: x86/mmu: Add dedicated API to map
 guest_memfd pfn into TDP MMU

On Wed, Oct 22, 2025 at 11:12:47AM -0700, Sean Christopherson wrote:
> On Wed, Oct 22, 2025, Yan Zhao wrote:
> > On Tue, Oct 21, 2025 at 09:36:52AM -0700, Sean Christopherson wrote:
> > > On Tue, Oct 21, 2025, Yan Zhao wrote:
> > > > On Thu, Oct 16, 2025 at 05:32:22PM -0700, Sean Christopherson wrote:
> > Is it good if we test is_page_fault_stale()? e.g.,
> No, because it can only get false positives, e.g. if an mmu_notifier invalidation
> on shared, non-guest_memfd memory.  Though a sanity check would be nice to have;
Right. The false positive is annoying.

> I believe we can simply do:
> 
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index c5734ca5c17d..440fd8f80397 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -1273,6 +1273,8 @@ int kvm_tdp_mmu_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
>         struct kvm_mmu_page *sp;
>         int ret = RET_PF_RETRY;
>  
> +       KVM_MMU_WARN_ON(!root || root->role.invalid);
> +
>         kvm_mmu_hugepage_adjust(vcpu, fault);
>  
>         trace_kvm_mmu_spte_requested(fault);
Ok.