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bh=8lNIJZw8YAjz68Gmod7C/9Iqybxq0zMLq+7ven4Sl20=; b=rd8PcoO7dO1r26AupmZg9g2ssXOh16XmgZxt/TK8TJJH1OgIhu6/lH9wA76S90K+LFMgrT VwL+SfBepqKw9QXHKIn8c8TrClQs2hVh5cG0JKZkdOcWtTcGFyqq5wtvF+I2lLA/DXUdq0 EWJtkZg5vKanMrt4rPUJyPH7YgHYHgI= Date: Wed, 1 Feb 2023 19:18:22 +0100 From: Borislav Petkov To: "Edgecombe, Rick P" Cc: "bsingharora@gmail.com" , "hpa@zytor.com" , "Syromiatnikov, Eugene" , "peterz@infradead.org" , "rdunlap@infradead.org" , "keescook@chromium.org" , "dave.hansen@linux.intel.com" , "kirill.shutemov@linux.intel.com" , "Eranian, Stephane" , "linux-mm@kvack.org" , "fweimer@redhat.com" , "nadav.amit@gmail.com" , "jannh@google.com" , "dethoma@microsoft.com" , "kcc@google.com" , "linux-arch@vger.kernel.org" , "pavel@ucw.cz" , "oleg@redhat.com" , "hjl.tools@gmail.com" , "Yang, Weijiang" , "Lutomirski, Andy" , "linux-doc@vger.kernel.org" , "arnd@arndb.de" , "tglx@linutronix.de" , "Schimpe, Christina" , "mike.kravetz@oracle.com" , "x86@kernel.org" , "akpm@linux-foundation.org" , "jamorris@linux.microsoft.com" , "john.allen@amd.com" , "rppt@kernel.org" , "andrew.cooper3@citrix.com" , "mingo@redhat.com" , "corbet@lwn.net" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "gorcunov@gmail.com" Subject: Re: [PATCH v5 06/39] x86/fpu: Add helper for modifying xstate Message-ID: References: <20230119212317.8324-1-rick.p.edgecombe@intel.com> <20230119212317.8324-7-rick.p.edgecombe@intel.com> <095e9694a682fc47ebedd34fddb660319549d6bb.camel@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <095e9694a682fc47ebedd34fddb660319549d6bb.camel@intel.com> X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: D46E018001A X-Stat-Signature: z6yguj7n1q883xkg5negtw731o1hdx3h X-Rspam-User: X-HE-Tag: 1675275516-20092 X-HE-Meta: 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 BTIXe8iD 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 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: On Wed, Feb 01, 2023 at 05:31:50PM +0000, Edgecombe, Rick P wrote: > On Wed, 2023-02-01 at 12:01 +0100, Borislav Petkov wrote: > > On Thu, Jan 19, 2023 at 01:22:44PM -0800, Rick Edgecombe wrote: > > > +void fpregs_lock_and_load(void) > > > +{ > > > + /* > > > + * fpregs_lock() only disables preemption (mostly). So > > > modifying state > > > + * in an interrupt could screw up some in progress fpregs > > > operation, > > > + * but appear to work. Warn about it. > > > > I don't like comments where it sounds like we don't know what we're > > doing. "Appear to work"? > > I can change it. This patch started with the observation that modifying > xstate from the kernel had been gotten wrong a couple times in the > past, so that is what this is referencing. Since then, the fancy > automatic solution got boiled down to this helper and a couple > warnings. Yeah, but that comment right now reads like: modifying in interrupt context can corrupt fpregs and you should not do it but it kinda works, by chance. Thus encouraging people to keep doing that. I guess "but appear to work" can go and then it is fine. Thx. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette