linux-kernel - Re: [PATCH v3 6/9] x86: prevent inline distortion by paravirt ops

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Message-ID: <20180611074507.GP12258@hirez.programming.kicks-ass.net>
Date:   Mon, 11 Jun 2018 09:45:07 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Nadav Amit <namit@...are.com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        Juergen Gross <jgross@...e.com>,
        Alok Kataria <akataria@...are.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH v3 6/9] x86: prevent inline distortion by paravirt ops

On Sun, Jun 10, 2018 at 07:19:08AM -0700, Nadav Amit wrote:
> +/*
> + * This generates an indirect call based on the operation type number.
> + * The type number, computed in PARAVIRT_PATCH, is derived from the
> + * offset into the paravirt_patch_template structure, and can therefore be
> + * freely converted back into a structure offset.
> + */
> +.macro PARAVIRT_ALT type:req clobber:req pv_opptr:req

Unlike the marcro maze you replaced, this has the CALL hardcoded in. So
maybe name this PARAVIRT_CALL instead of PARAVIRT_ALT ?

> +771:	ANNOTATE_RETPOLINE_SAFE
> +	call *\pv_opptr
> +772:	.pushsection .parainstructions,"a"
> +	_ASM_ALIGN
> +	_ASM_PTR 771b
> +	.byte \type
> +	.byte 772b-771b
> +	.short \clobber
> +	.popsection
> +.endm