linux-kernel - Re: [PATCH v4 6/8] mm: Introduce deferred freeing for kernel page tables

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Message-ID: <20250915113509.GA1024672@nvidia.com>
Date: Mon, 15 Sep 2025 08:35:09 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>,
	Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
	Jann Horn <jannh@...gle.com>, Vasant Hegde <vasant.hegde@....com>,
	"Hansen, Dave" <dave.hansen@...el.com>,
	Alistair Popple <apopple@...dia.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Uladzislau Rezki <urezki@...il.com>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Andy Lutomirski <luto@...nel.org>, "Lai, Yi1" <yi1.lai@...el.com>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"security@...nel.org" <security@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v4 6/8] mm: Introduce deferred freeing for kernel page
 tables

On Fri, Sep 12, 2025 at 08:17:23AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@...dia.com>
> > Sent: Saturday, September 6, 2025 2:44 AM
> > 
> > On Fri, Sep 05, 2025 at 01:51:01PM +0800, Lu Baolu wrote:
> > 
> > > +	list_for_each_entry_safe(pt, next, &page_list, pt_list) {
> > > +		list_del(&pt->pt_list);
> > 
> > The list_del isn't necessary, it doesn't zero the list, just _safe
> > iteration is fine.
> > 
> 
> if no list_del why need to keep the _safe iteration? 

__pagetable_free() can change the memory holding pt->pt-list, it is
like kfree. So _safe is needed to allow that.

_safe is not just about deletion, anything that could change the list
element must use a safe iteration.

Jason