linux-kernel - Re: [PATCH] mm/x86/pat: Only untrack the pfn range if unmap region

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Message-ID: <1dc7cf79-4c01-4b1e-be33-49eb2bdb9238@redhat.com>
Date: Wed, 17 Jul 2024 18:32:05 +0200
From: David Hildenbrand <david@...hat.com>
To: Peter Xu <peterx@...hat.com>
Cc: Yan Zhao <yan.y.zhao@...el.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "linux-mm@...ck.org" <linux-mm@...ck.org>,
 Andrew Morton <akpm@...ux-foundation.org>,
 Alex Williamson <alex.williamson@...hat.com>,
 Jason Gunthorpe <jgg@...dia.com>, Al Viro <viro@...iv.linux.org.uk>,
 Dave Hansen <dave.hansen@...ux.intel.com>, Andy Lutomirski
 <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, "Kirill A . Shutemov"
 <kirill@...temov.name>, "x86@...nel.org" <x86@...nel.org>,
 "Tian, Kevin" <kevin.tian@...el.com>, Pei Li <peili.dev@...il.com>,
 David Wang <00107082@....com>, Bert Karwatzki <spasswolf@....de>,
 Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH] mm/x86/pat: Only untrack the pfn range if unmap region

On 17.07.24 18:30, Peter Xu wrote:
> On Wed, Jul 17, 2024 at 04:17:12PM +0200, David Hildenbrand wrote:
>> I'd be curious how a previous truncation on a file can tear down a PFNMAP
>> mapping -- and if there are simple ways to forbid that (if possible).
> 
> Unfortunately, forbiding it may not work for vfio, as vfio would like to
> allow none (or partial) mapping on the bars.. at least so far that's the
> plan.

I think vfio should handle that memtype reservation manually, as you 
proposed. So that shouldn't block that IIUC.

-- 
Cheers,

David / dhildenb