linux-kernel - Re: [RFC PATCH 8/8] kvm: gmem: Allow restricted userspace mappings

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Message-ID: <47ce1b10-e031-4ac1-b88f-9d4194533745@redhat.com>
Date: Tue, 9 Jul 2024 23:13:25 +0200
From: David Hildenbrand <david@...hat.com>
To: Fuad Tabba <tabba@...gle.com>, Patrick Roy <roypat@...zon.co.uk>
Cc: seanjc@...gle.com, pbonzini@...hat.com, akpm@...ux-foundation.org,
 dwmw@...zon.co.uk, rppt@...nel.org, tglx@...utronix.de, mingo@...hat.com,
 bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
 willy@...radead.org, graf@...zon.com, derekmn@...zon.com,
 kalyazin@...zon.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, dmatlack@...gle.com, chao.p.peng@...ux.intel.com,
 xmarcalx@...zon.co.uk
Subject: Re: [RFC PATCH 8/8] kvm: gmem: Allow restricted userspace mappings

On 09.07.24 16:48, Fuad Tabba wrote:
> Hi Patrick,
> 
> On Tue, Jul 9, 2024 at 2:21 PM Patrick Roy <roypat@...zon.co.uk> wrote:
>>
>> Allow mapping guest_memfd into userspace. Since AS_INACCESSIBLE is set
>> on the underlying address_space struct, no GUP of guest_memfd will be
>> possible.
> 
> This patch allows mapping guest_memfd() unconditionally. Even if it's
> not guppable, there are other reasons why you wouldn't want to allow
> this. Maybe a config flag to gate it? e.g.,


As discussed with Jason, maybe not the direction we want to take with 
guest_memfd.
If it's private memory, it shall not be mapped. Also not via magic 
config options.

We'll likely discuss some of that in the meeting MM tomorrow I guess 
(having both shared and private memory in guest_memfd).

Note that just from staring at this commit, I don't understand the 
motivation *why* we would want to do that.

-- 
Cheers,

David / dhildenb