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Message-ID: <20190401082424.uljjh5cejj33gb3r@linutronix.de> Date: Mon, 1 Apr 2019 10:24:24 +0200 From: Sebastian Andrzej Siewior <bigeasy@...utronix.de> To: Thomas Gleixner <tglx@...utronix.de> Cc: linux-kernel@...r.kernel.org, x86@...nel.org, Andy Lutomirski <luto@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, Radim Krčmář <rkrcmar@...hat.com>, kvm@...r.kernel.org, "Jason A. Donenfeld" <Jason@...c4.com>, Rik van Riel <riel@...riel.com>, Dave Hansen <dave.hansen@...ux.intel.com> Subject: Re: [PATCH 18/24] x86/fpu: Prepare copy_fpstate_to_sigframe() for TIF_NEED_FPU_LOAD On 2019-03-31 20:20:25 [+0200], Thomas Gleixner wrote: > > I think this should do the following: > > fpregs_lock(); > if (!test_thread_flag(TIF_NEED_FPU_LOAD)) { > pagefault_disable(); > ret = copy_fpu_to_user(...); > pagefault_enable(); > if (!res) > return 0; > copy_fpregs_to_fpstate(fpu); > } > fpregs_unlock(); > > The point is that in most cases the direct store from the FPU registers to > user space will succeed simply because the stack is accessible and you only > do the store in kernel memory and copy when that fails. let me try that. > Thanks, > > tglx > Sebastian
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