linux-kernel - Re: [RFC PATCH v5 02/45] KVM: x86/mmu: Update iter->old

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Message-ID: <1c4bdb3613ebaf65b5dcf9a2268b06fa0c5a6ef3.camel@intel.com>
Date: Tue, 3 Feb 2026 10:30:47 +0000
From: "Huang, Kai" <kai.huang@...el.com>
To: "seanjc@...gle.com" <seanjc@...gle.com>, "x86@...nel.org"
	<x86@...nel.org>, "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>, "kas@...nel.org" <kas@...nel.org>,
	"bp@...en8.de" <bp@...en8.de>, "mingo@...hat.com" <mingo@...hat.com>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>, "tglx@...nel.org"
	<tglx@...nel.org>
CC: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>, "ackerleytng@...gle.com"
	<ackerleytng@...gle.com>, "sagis@...gle.com" <sagis@...gle.com>, "Annapurve,
 Vishal" <vannapurve@...gle.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Zhao, Yan Y" <yan.y.zhao@...el.com>, "Li,
 Xiaoyao" <xiaoyao.li@...el.com>, "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>, "Yamahata, Isaku"
	<isaku.yamahata@...el.com>, "binbin.wu@...ux.intel.com"
	<binbin.wu@...ux.intel.com>
Subject: Re: [RFC PATCH v5 02/45] KVM: x86/mmu: Update iter->old_spte if
 cmpxchg64 on mirror SPTE "fails"

On Wed, 2026-01-28 at 17:14 -0800, Sean Christopherson wrote:
> Pass a pointer to iter->old_spte, not simply its value, when setting an
> external SPTE in __tdp_mmu_set_spte_atomic(), so that the iterator's value
> will be updated if the cmpxchg64 to freeze the mirror SPTE fails.  The bug
> is currently benign as TDX is mutualy exclusive with all paths that do
> "local" retry", e.g. clear_dirty_gfn_range() and wrprot_gfn_range().
> 
> Fixes: 77ac7079e66d ("KVM: x86/tdp_mmu: Propagate building mirror page tables")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>

Reviewed-by: Kai Huang <kai.huang@...el.com>

Btw, do we need to cc stable?