linux-kernel - Re: [PATCHv6 06/30] x86/traps: Refactor exc_general

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Message-ID: <87a6dp2ztq.ffs@tglx>
Date:   Thu, 17 Mar 2022 01:21:53 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...el.com,
        luto@...nel.org, peterz@...radead.org
Cc:     sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        thomas.lendacky@....com, brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCHv6 06/30] x86/traps: Refactor exc_general_protection()

On Wed, Mar 16 2022 at 05:08, Kirill A. Shutemov wrote:
> TDX brings a new exception -- Virtualization Exception (#VE). Handling
> of #VE structurally very similar to handling #GP.
>
> Extract two helpers from exc_general_protection() that can be reused for
> handling #VE.
>
> No functional changes.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Reviewed-by: Dave Hansen <dave.hansen@...ux.intel.com>

Not that I care much, but this is the second instance of something I
suggested. We have tags for that...

> +static bool gp_try_fixup_and_notify(struct pt_regs *regs, int trapnr,
> +				    unsigned long error_code, const char *str)
> +{
> +	int ret;

Adding this to make my suggestion compile is the easy way out, but...

> +
> +	if (fixup_exception(regs, trapnr, error_code, 0))
> +		return true;
> +
> +	current->thread.error_code = error_code;
> +	current->thread.trap_nr = trapnr;
> +
> +	/*
> +	 * To be potentially processing a kprobe fault and to trust the result
> +	 * from kprobe_running(), we have to be non-preemptible.
> +	 */
> +	if (!preemptible() && kprobe_running() &&
> +	    kprobe_fault_handler(regs, trapnr))
> +		return true;
> +
> +	ret = notify_die(DIE_GPF, str, regs, error_code, trapnr, SIGSEGV);
> +	return ret == NOTIFY_STOP;

Why not doing the obvious:

	return notify_die(DIE_GPF, str, regs, error_code, trapnr, SIGSEGV) == NOTIFY_STOP;

Hmm?

Thanks,

        tglx