linux-kernel - Re: [PATCH v4 06/16] x86/virt/tdx: Improve PAMT refcounts allocation for sparse memory

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <21a759efdcfb4429ed952303f7d7143263220b22.camel@intel.com>
Date: Wed, 26 Nov 2025 20:47:19 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>
CC: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "linux-coco@...ts.linux.dev"
	<linux-coco@...ts.linux.dev>, "Huang, Kai" <kai.huang@...el.com>, "Li,
 Xiaoyao" <xiaoyao.li@...el.com>, "Hansen, Dave" <dave.hansen@...el.com>,
	"Zhao, Yan Y" <yan.y.zhao@...el.com>, "Wu, Binbin" <binbin.wu@...el.com>,
	"kas@...nel.org" <kas@...nel.org>, "seanjc@...gle.com" <seanjc@...gle.com>,
	"mingo@...hat.com" <mingo@...hat.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "pbonzini@...hat.com" <pbonzini@...hat.com>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>, "tglx@...utronix.de"
	<tglx@...utronix.de>, "Annapurve, Vishal" <vannapurve@...gle.com>, "Gao,
 Chao" <chao.gao@...el.com>, "bp@...en8.de" <bp@...en8.de>, "x86@...nel.org"
	<x86@...nel.org>
Subject: Re: [PATCH v4 06/16] x86/virt/tdx: Improve PAMT refcounts allocation
 for sparse memory

On Tue, 2025-11-25 at 11:15 +0800, Binbin Wu wrote:
> On 11/21/2025 8:51 AM, Rick Edgecombe wrote:
> [...]
> > +
> > +/* Unmap a page from the PAMT refcount vmalloc region */
> > +static int pamt_refcount_depopulate(pte_t *pte, unsigned long addr, void *data)
> > +{
> > +	struct page *page;
> > +	pte_t entry;
> > +
> > +	spin_lock(&init_mm.page_table_lock);
> > +
> > +	entry = ptep_get(pte);
> > +	/* refcount allocation is sparse, may not be populated */
> 
> Not sure this comment about "sparse" is accurate since this function is called via
> apply_to_existing_page_range().
> 
> And the check for not present just for sanity check?

Yes, I don't see what that comment is referring to. But we do need it, because
hypothetically the refcount mapping could have failed halfway. So we will have
pte_none()s for the ranges that didn't get populated. I'll use:

/* Refcount mapping could have failed part way, handle aborted mappings. */