linux-kernel - Re: [PATCH v4 06/39] x86/fpu: Add helper for modifying xstate

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Message-ID: <Y6Gk1CcK/dHWqaVA@zn.tnic>
Date:   Tue, 20 Dec 2022 13:04:36 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Rick Edgecombe <rick.p.edgecombe@...el.com>
Cc:     x86@...nel.org, "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H . J . Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        Weijiang Yang <weijiang.yang@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        John Allen <john.allen@....com>, kcc@...gle.com,
        eranian@...gle.com, rppt@...nel.org, jamorris@...ux.microsoft.com,
        dethoma@...rosoft.com, akpm@...ux-foundation.org,
        Andrew.Cooper3@...rix.com, christina.schimpe@...el.com
Subject: Re: [PATCH v4 06/39] x86/fpu: Add helper for modifying xstate

On Fri, Dec 02, 2022 at 04:35:33PM -0800, Rick Edgecombe wrote:
> +void fpregs_lock_and_load(void)

Fun naming :)

> +{
> +	/*
> +	 * fpregs_lock() only disables preemption (mostly). So modifing state

Unknown word [modifing] in comment.
Suggestions: ['modifying',...

> +	 * in an interrupt could screw up some in progress fpregs operation,
> +	 * but appear to work. Warn about it.
> +	 */
> +	WARN_ON_ONCE(!irq_fpu_usable());
> +	WARN_ON_ONCE(current->flags & PF_KTHREAD);
> +
> +	fpregs_lock();

So it locks them here...

/me goes further into the patchset

aha, and the counterpart of this function is fpregs_unlock() so
everything gets sandwitched between the two.

Ok, I guess.

> +EXPORT_SYMBOL_GPL(fpregs_lock_and_load);

Exported for KVM?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette