linux-kernel - Re: [PATCH 05/10] guestmemfs: add file mmap callback

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Message-ID: <20241101134202.GB35848@ziepe.ca>
Date: Fri, 1 Nov 2024 10:42:02 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: "Gowans, James" <jgowans@...zon.com>
Cc: "quic_eberman@...cinc.com" <quic_eberman@...cinc.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"rppt@...nel.org" <rppt@...nel.org>,
	"brauner@...nel.org" <brauner@...nel.org>,
	"anthony.yznaga@...cle.com" <anthony.yznaga@...cle.com>,
	"steven.sistare@...cle.com" <steven.sistare@...cle.com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"seanjc@...gle.com" <seanjc@...gle.com>,
	"Durrant, Paul" <pdurrant@...zon.co.uk>,
	"pbonzini@...hat.com" <pbonzini@...hat.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"Woodhouse, David" <dwmw@...zon.co.uk>,
	"Saenz Julienne, Nicolas" <nsaenz@...zon.es>,
	"viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>,
	"Graf (AWS), Alexander" <graf@...zon.de>,
	"jack@...e.cz" <jack@...e.cz>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH 05/10] guestmemfs: add file mmap callback

On Fri, Nov 01, 2024 at 01:01:00PM +0000, Gowans, James wrote:

> Thanks Jason, that sounds perfect. I'll work on the next rev which will:
> - expose a filesystem which owns reserved/persistent memory, just like
> this patch.

Is this step needed?

If the guest memfd is already told to get 1G pages in some normal way,
why do we need a dedicated pool just for the KHO filesystem?

Back to my suggestion, can't KHO simply freeze the guest memfd and
then extract the memory layout, and just use the normal allocator?

Or do you have a hard requirement that only KHO allocated memory can
be preserved across kexec?

Jason