linux-kernel - Re: [PATCH 1/8] kasan,x86: Frob kasan

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Date:   Wed, 6 Mar 2019 18:14:51 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Julien Thierry <julien.thierry@....com>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...capital.net>,
        Ingo Molnar <mingo@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        James Morse <james.morse@....com>, valentin.schneider@....com,
        Brian Gerst <brgerst@...il.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>, jgross@...e.com
Subject: Re: [PATCH 1/8] kasan,x86: Frob kasan_report() in an exception

On Wed, Mar 06, 2019 at 02:13:47PM +0100, Peter Zijlstra wrote:
> +static __always_inline unsigned long smap_save(void)
> +{
> +	unsigned long flags = arch_local_save_flags();
> +	clac();
> +	return flags;
> +}
> +
> +static __always_inline void smap_restore(unsigned long flags)
> +{
> +	arch_local_irq_restore(flags);
> +}

ARGH; the bloody paravirt me harder nonsense makes that pvops calls.

And that (obviously) explodes.. Anybody got any clue why that Xen
trainwreck wants to paravirt: "PUSHF;POP" and "PUSH;POPF" !?

Also; I suppose I can ALTERNATIVE the whole thing, because Xen will not
be having SMAP in the first place I suppose.