Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:8 as permitted sender) client-ip=2620:137:e000::3:8;
MIME-Version: 1.0
References: <20230915105933.495735-1-matteorizzo@google.com>
 <7a4f5128-28fd-3c5f-34c2-1c34f4448174@intel.com> <1d7573c0-ebbc-6ed2-f152-1045eb0542f9@os.amperecomputing.com>
 <CAHKB1w+rVyww0UrHhzeGfPA7FM482Z-7ApzXvekVqLHvTDAV3Q@mail.gmail.com> <ZQiLX0W2Tcr+wdJT@gmail.com>
In-Reply-To: <ZQiLX0W2Tcr+wdJT@gmail.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Mon, 18 Sep 2023 11:05:31 -0700
Message-ID: <CAHk-=wgGzB4u-WZsDpdgjwX1w5=9CLE0gorhaNFD09P1FUGeuQ@mail.gmail.com>
Subject: Re: [RFC PATCH 00/14] Prevent cross-cache attacks in the SLUB allocator
To:     Ingo Molnar <mingo@kernel.org>
Cc:     Matteo Rizzo <matteorizzo@google.com>,
        "Lameter, Christopher" <cl@os.amperecomputing.com>,
        Dave Hansen <dave.hansen@intel.com>, penberg@kernel.org,
        rientjes@google.com, iamjoonsoo.kim@lge.com,
        akpm@linux-foundation.org, vbabka@suse.cz,
        roman.gushchin@linux.dev, 42.hyeyoo@gmail.com,
        keescook@chromium.org, linux-kernel@vger.kernel.org,
        linux-doc@vger.kernel.org, linux-mm@kvack.org,
        linux-hardening@vger.kernel.org, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        x86@kernel.org, hpa@zytor.com, corbet@lwn.net, luto@kernel.org,
        peterz@infradead.org, jannh@google.com, evn@google.com,
        poprdi@google.com, jordyzomer@google.com
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Mon, 18 Sept 2023 at 10:39, Ingo Molnar <mingo@kernel.org> wrote:
>
> What's the split of the increase in overhead due to SLAB_VIRTUAL=y, between
> user-space execution and kernel-space execution?

... and equally importantly, what about DMA?

Or what about the fixed-size slabs (aka kmalloc?) What's the point of
"never re-use the same address for a different slab", when the *same*
slab will contain different kinds of allocations anyway?

I think the whole "make it one single compile-time option" model is
completely and fundamentally broken.

                     Linus