Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.37 as permitted sender) client-ip=23.128.96.37;
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> <CAHk-=wgGzB4u-WZsDpdgjwX1w5=9CLE0gorhaNFD09P1FUGeuQ@mail.gmail.com>
 <CAHKB1w+9GgY_e6J+rZ4zDaXrPZab5xteTuDEH0Z2hWe6x-pT5g@mail.gmail.com>
In-Reply-To: <CAHKB1w+9GgY_e6J+rZ4zDaXrPZab5xteTuDEH0Z2hWe6x-pT5g@mail.gmail.com>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 19 Sep 2023 11:49:48 -0700
Message-ID: <CAHk-=wiWReaH-khCA_uiKC5xJSQkDudEfybdepSZXKvdXZkZsg@mail.gmail.com>
Subject: Re: [RFC PATCH 00/14] Prevent cross-cache attacks in the SLUB allocator
To:     Matteo Rizzo <matteorizzo@google.com>
Cc:     Ingo Molnar <mingo@kernel.org>,
        "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 Tue, 19 Sept 2023 at 08:48, Matteo Rizzo <matteorizzo@google.com> wrote:
>
> On Mon, 18 Sept 2023 at 20:05, Linus Torvalds
> <torvalds@linux-foundation.org> wrote:
> >
> > ... and equally importantly, what about DMA?
>
> I'm not exactly sure what you mean by this, I don't think this should
> affect the performance of DMA.

I was more worried about just basic correctness.

We've traditionally had a lot of issues with using virtual addresses
for dma, simply because we've got random drivers, and I'm not entirely
convinced that your "virt_to_phys()" update will catch it all.

IOW, even on x86-64 - which is hopefully better than most
architectures because it already has that double mapping issue - we
have things like

        unsigned long paddr = (unsigned long)vaddr - __PAGE_OFFSET;

in other places than just the __phys_addr() code.

The one place I grepped for looks to be just boot-time AMD memory
encryption, so wouldn't be any slab allocation, but ...

               Linus