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Thu, 23 Oct 2025 10:42:50 -0700 (PDT) MIME-Version: 1.0 References: <20251017141536.577466-1-kirill@shutemov.name> In-Reply-To: From: Yang Shi Date: Thu, 23 Oct 2025 10:42:37 -0700 X-Gm-Features: AWmQ_bl7HHHe3F5m7s8SKqaEwkR90lx0Ku2nfc1LYSRH2AGyQ13C81borZW52B8 Message-ID: Subject: Re: [PATCH] mm/filemap: Implement fast short reads To: Kiryl Shutsemau Cc: David Hildenbrand , Andrew Morton , Matthew Wilcox , Linus Torvalds , Alexander Viro , Christian Brauner , Jan Kara , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: CFEF5100010 X-Stat-Signature: ytfyhdmhfe13i3zg43jfzd9uri4pkipe X-Rspam-User: X-HE-Tag: 1761241371-237689 X-HE-Meta: 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 S3FPEV88 4eIgvcFLDHVpBorCt9/5bTlX/z6QxWavsOfJtyrsW0FYNQ6wlNtHktOMK6NgwJQ3NF6YN4cTo5bUPwRo4RoIac8DwiN7ibq/xmtOq5XlnKlVwaJkw5+v87D2D3bG37UK/XzNw4IoDEApWHIW34xeKoae41D1TL8O/hYtJSC9rL9e0zVhVgRQEawhhk5yMEG74fnHrD3NbgiUMCxfreeFXobNjX97H2BdCVSttV1GHFLb/Tao2KraHqWy2Yov2ys/QLkU7ZW7xR25a2gavnKucaizEXnskpaijxcFtrtpFD46kSPB/Y3uLj3mXsD7tDxehOI/f X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Oct 23, 2025 at 3:34=E2=80=AFAM Kiryl Shutsemau wrote: > > On Wed, Oct 22, 2025 at 07:28:27PM +0200, David Hildenbrand wrote: > > "garbage" as in pointing at something without a direct map, something t= hat's > > protected differently (MTE? weird CoCo protection?) or even worse MMIO = with > > undesired read-effects. > > Pedro already points to the problem with missing direct mapping. > _nofault() copy should help with this. > > Can direct mapping ever be converted to MMIO? It can be converted to DMA > buffer (which is fine), but MMIO? I have not seen it even in virtualized > environments. > > I cannot say for all CoCo protections, but TDX guest shared<->private > should be fine. > > I am not sure about MTE. Is there a way to bypass MTE check for a load? > And how does it deal with stray reads from load_unaligned_zeropad()? If I remember correctly, _nofault() copy should skip tag check too. Thanks, Yang > > -- > Kiryl Shutsemau / Kirill A. Shutemov >