linux-kernel - Re: [RFC PATCH 13/22] x86/fpu/xstate: Expand dynamic user state area on first use

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Message-ID: <20201014104148.GD2628@hirez.programming.kicks-ass.net>
Date:   Wed, 14 Oct 2020 12:41:48 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     "Brown, Len" <len.brown@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        "Bae, Chang Seok" <chang.seok.bae@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        X86 ML <x86@...nel.org>, "Liu, Jing2" <jing2.liu@...el.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 13/22] x86/fpu/xstate: Expand dynamic user state area
 on first use

On Tue, Oct 13, 2020 at 03:43:59PM -0700, Dave Hansen wrote:
> On 10/13/20 3:31 PM, Brown, Len wrote:
> > vmalloc() does not fail, and does not return an error, and so there is no concept
> > of returning a signal.
> 
> Well, the order-0 allocations are no-fail, as are the vmalloc kernel
> structures and the page tables that might have to be allocated.  But,
> that's not guaranteed to be in place *forever*.  I think we still need
> to check for and handle allocation failures, even if they're not known
> to be possible today.

Quite, on top of that, we could run out of vmalloc space (unlikely, but
sitll).

You really have to deal with vmalloc() failing.