linux-kernel - RE: [PATCH] udmabuf: revert 'Add support for mapping hugepages (v4)'

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Message-ID: <89652021ecea4aa2ada763c97deeb543@AcuMS.aculab.com>
Date:   Tue, 13 Jun 2023 12:25:03 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     "'Kasireddy, Vivek'" <vivek.kasireddy@...el.com>,
        David Hildenbrand <david@...hat.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        Hugh Dickins <hughd@...gle.com>
CC:     Gerd Hoffmann <kraxel@...hat.com>,
        "Kim, Dongwon" <dongwon.kim@...el.com>,
        "Chang, Junxiao" <junxiao.chang@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Hocko, Michal" <mhocko@...e.com>,
        "jmarchan@...hat.com" <jmarchan@...hat.com>,
        "muchun.song@...ux.dev" <muchun.song@...ux.dev>,
        James Houghton <jthoughton@...gle.com>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: RE: [PATCH] udmabuf: revert 'Add support for mapping hugepages (v4)'

From: Kasireddy, Vivek <vivek.kasireddy@...el.com>
> Sent: 13 June 2023 09:26
...
> > Is my understanding correct, that we can effectively long-term pin
> > (worse than mlock) 64 MiB per UDMABUF_CREATE, allowing eventually !root
> > users
>
> The 64 MiB limit is the theoretical upper bound that we have not seen hit in
> practice. Typically, for a 1920x1080 resolution (commonly used in Guests),
> the size of the FB is ~8 MB (1920x1080x4). And, most modern Graphics
> compositors flip between two FBs.

What code does and what potentially malicious code might do
are entirely different things.

	David

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