linux-kernel - Re: [PATCH v5 6/8] mm: Introduce deferred freeing for kernel page tables

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Message-ID: <4858074d-f058-41ec-a581-a8254b8cc2d7@redhat.com>
Date: Thu, 9 Oct 2025 21:28:58 +0200
From: David Hildenbrand <david@...hat.com>
To: Lu Baolu <baolu.lu@...ux.intel.com>, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Kevin Tian <kevin.tian@...el.com>, Jason Gunthorpe <jgg@...dia.com>,
 Jann Horn <jannh@...gle.com>, Vasant Hegde <vasant.hegde@....com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <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>, Yi Lai <yi1.lai@...el.com>
Cc: iommu@...ts.linux.dev, security@...nel.org, x86@...nel.org,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org,
 Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v5 6/8] mm: Introduce deferred freeing for kernel page
 tables

On 19.09.25 07:40, Lu Baolu wrote:
> From: Dave Hansen <dave.hansen@...ux.intel.com>
> 
> This introduces a conditional asynchronous mechanism, enabled by
> CONFIG_ASYNC_PGTABLE_FREE. When enabled, this mechanism defers the freeing
> of pages that are used as page tables for kernel address mappings. These
> pages are now queued to a work struct instead of being freed immediately.
> 
> This deferred freeing provides a safe context for a future patch to add
> an IOMMU-specific callback, which might be expensive on large-scale
> systems. This ensures the necessary IOMMU cache invalidation is performed
> before the page is finally returned to the page allocator outside of any
> critical, non-sleepable path.
> 
> Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
> Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> ---

Can we please squash #7 in here and make sure to call the config knob 
something that indicates that it is for *kernel* page tables only?

ASYNC_KERNEL_PGTABLE_FREE

or sth like that.

-- 
Cheers

David / dhildenb