linux-kernel - Re: [PATCH 14/22] x86/fpu: Eager switch PKRU state

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Message-ID: <20190321171005.l3sywcudjvxmi27n@linutronix.de>
Date:   Thu, 21 Mar 2019 18:10:05 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Dave Hansen <dave.hansen@...el.com>
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 14/22] x86/fpu: Eager switch PKRU state

On 2019-03-12 17:06:18 [-0700], Dave Hansen wrote:
> Thanks for doing this.  I'll see if I can dig into the test case and
> figure out why it's not doing what I expected.  It might be that the CPU
> _could_ go back to the init state but chooses not to, or that something
> else is taking us out of the init state before we reach the kernel code
> in question.

I'm going to drop that WARN_ON() check. The reason is that we are fully
preemptible during fpstate_init() and a context switch during memset()
and fpstate_init_xstate() triggers this warning.

Sebastian