linux-kernel - Re: [patch V6 10/37] x86/entry: Switch XEN/PV hypercall entry to IDTENTRY

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Date:   Wed, 20 May 2020 22:23:18 -0400
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Andrew Cooper <andrew.cooper3@...rix.com>,
        LKML <linux-kernel@...r.kernel.org>, X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V6 10/37] x86/entry: Switch XEN/PV hypercall entry to
 IDTENTRY

On 5/20/20 3:16 PM, Thomas Gleixner wrote:


> +__visible noinstr void xen_pv_evtchn_do_upcall(struct pt_regs *regs)
> +{
> +	struct pt_regs *old_regs;
> +	bool inhcall;
> +
> +	idtentry_enter(regs);
> +	old_regs = set_irq_regs(regs);
> +
> +	run_on_irqstack(__xen_pv_evtchn_do_upcall, NULL, regs);


We need to handle nested case (i.e. !irq_needs_irq_stack(), like in your
original version). Moving get_and_clear_inhcall() up should prevent
scheduling when this happens.


-boris


> +
> +	set_irq_regs(old_regs);
> +
> +	inhcall = get_and_clear_inhcall();
> +	__idtentry_exit(regs, inhcall);
> +	restore_inhcall(inhcall);
>  }