linux-kernel - Re: [PATCH v4 5/8] x86/mm: Use pagetable

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Message-ID: <eced5393-16f1-4756-9703-3bae05160ade@linux.intel.com>
Date: Fri, 19 Sep 2025 13:31:18 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Dave Hansen <dave.hansen@...el.com>, Jason Gunthorpe <jgg@...dia.com>
Cc: Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>, Kevin Tian <kevin.tian@...el.com>,
 Jann Horn <jannh@...gle.com>, Vasant Hegde <vasant.hegde@....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>,
 iommu@...ts.linux.dev, security@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 5/8] x86/mm: Use pagetable_free()

On 9/6/25 04:11, Dave Hansen wrote:
> On 9/5/25 11:41, Jason Gunthorpe wrote:
>>> --- a/arch/x86/mm/init_64.c
>>> +++ b/arch/x86/mm/init_64.c
>>> @@ -1013,7 +1013,7 @@ static void __meminit free_pagetable(struct page *page, int order)
>>>   		free_reserved_pages(page, nr_pages);
>>>   #endif
>>>   	} else {
>>> -		free_pages((unsigned long)page_address(page), order);
>>> +		pagetable_free(page_ptdesc(page));
>>>   	}
>>>   }
>> Er.. So if bootmem happens to be under the table and we happen to free
>> it due to memory hotplug we don't go through the SVA fixing path?
>>
>> Seems wrong??
> 
> On second thought...
> 
> Yes, freeing bootmem with no SVA fixing is wrong. It should be fixed.
> Period. But, it's wrong one time for something super rare: memory unplug
> of memory that was present at boot. It also can't be triggered by
> unprivileged users.
> 
> As-is, this series fixes vfree(). That path is not nearly rare, can
> happen an arbitrary number of times on each boot, and might even be
> triggered by folks that are less than root.
> 
> So I kinda think we should just make clear that this series leaves
> _some_ holes, but I do think it should go in mostly as-is.
> 

Okay, I will put this in the commit message and update this series with
a new version.

Thanks,
baolu