linux-kernel - Re: [PATCH] x86/irq: Preserve vector in orig

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Date:   Wed, 26 Aug 2020 20:30:25 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Alexander Graf <graf@...zon.com>, X86 ML <x86@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        "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>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.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>,
        Avi Kivity <avi@...lladb.com>,
        "Herrenschmidt\, Benjamin" <benh@...zon.com>, robketr@...zon.de,
        amos@...lladb.com, Brian Gerst <brgerst@...il.com>,
        stable@...r.kernel.org
Subject: Re: [PATCH] x86/irq: Preserve vector in orig_ax for APIC code

On Wed, Aug 26 2020 at 18:33, Alexander Graf wrote:
> On 26.08.20 16:27, Thomas Gleixner wrote:
>> The below nasty hack cures it, but I hate it with a passion. I'll look
>> deeper for a sane variant.
>
> An alternative (that doesn't make the code easier to read, but would fix 
> the issue at hand) would be touse a pushq imm16 with vector | 0x8000 
> instead to always make the value negative, no?

Which makes each entry larger than 8 byte which was frowned upon before.

And it does not solve the issue that we abuse orig_ax which Andy
mentioned.

Thanks,

        tglx