linux-kernel - Re: [tip:x86/fpu] x86/fpu: Fault-in user stack if copy_fpstate_to

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Date:   Tue, 30 Apr 2019 07:20:21 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     jannh@...gle.com, bp@...e.de, riel@...riel.com,
        bigeasy@...utronix.de, linux-kernel@...r.kernel.org, hpa@...or.com,
        pbonzini@...hat.com, tglx@...utronix.de, kvm@...r.kernel.org,
        luto@...capital.net, kurt.kanzenbach@...utronix.de, x86@...nel.org,
        mingo@...nel.org, linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/fpu] x86/fpu: Fault-in user stack if
 copy_fpstate_to_sigframe() fails

On 4/29/19 11:52 AM, tip-bot for Sebastian Andrzej Siewior wrote:
> Instead of utilizing copy_xstate_to_user(), fault-in the user memory
> and retry the fast path. Ideally, the fast path succeeds on the second
> attempt but may be retried again if the memory is swapped out due
> to memory pressure. If the user memory can not be faulted-in then
> get_user_pages() returns an error so we don't loop forever.
> 
> Fault in memory via get_user_pages() so copy_fpregs_to_sigframe()
> succeeds without a fault.

Thanks for reworking this.  It looks great.

Acked-by: Dave Hansen <dave.hansen@...el.com>