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Date: Sun, 10 May 2020 10:46:25 +0200 From: Borislav Petkov <bp@...en8.de> To: Yu-cheng Yu <yu-cheng.yu@...el.com> Cc: linux-kernel@...r.kernel.org, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, Tony Luck <tony.luck@...el.com>, Andy Lutomirski <luto@...nel.org>, Rik van Riel <riel@...riel.com>, "Ravi V. Shankar" <ravi.v.shankar@...el.com>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Fenghua Yu <fenghua.yu@...el.com>, Peter Zijlstra <peterz@...radead.org> Subject: Re: [PATCH v3 09/10] x86/fpu/xstate: Preserve supervisor states for slow path of __fpu__restore_sig() On Sat, Mar 28, 2020 at 09:43:06AM -0700, Yu-cheng Yu wrote: > The signal return code is responsible for taking an XSAVE buffer present > in user memory and loading it into the hardware registers. This > operation only affects user XSAVE state and never affects supervisor state. > > The fast path through this code simply points XRSTOR directly at the > user buffer. However, due to page faults, this XRSTOR can fail. If it ^^^^^^^^^^^^^^^^^^ "However, since user memory is not guaranteed to be always mapped, ... " > fails, the signal return code falls back to a slow path which can > tolerate page faults. > > That slow path copies the xfeatures one by one out of the user buffer > into the task's fpu state area. However, by being in a context where it > can handle page faults, the code can also schedule. That exposes us to ^^ Pls use passive voice in your commit message: no "we" or "I", etc, and describe your changes in imperative mood. Fix this in all your commit messages pls. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette
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