linux-kernel - Re: [RFC PATCH v2 21/34] x86/msr: Utilize the alternatives mechanism to write MSR

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Message-ID: <20250425071157.GI18306@noisy.programming.kicks-ass.net>
Date: Fri, 25 Apr 2025 09:11:57 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Jürgen Groß <jgross@...e.com>
Cc: "Xin Li (Intel)" <xin@...or.com>, linux-kernel@...r.kernel.org,
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Subject: Re: [RFC PATCH v2 21/34] x86/msr: Utilize the alternatives mechanism
 to write MSR

On Tue, Apr 22, 2025 at 11:57:01AM +0200, Jürgen Groß wrote:
> On 22.04.25 10:22, Xin Li (Intel) wrote:

> >    This becomes even more silly for trivial instructions like STI/CLI
> >    or in the worst case paravirt_nop().
> 
> This is nonsense.

What Jurgen says. Someone hasn't done their homework.

static __always_inline void arch_local_irq_disable(void)
{
        PVOP_ALT_VCALLEE0(irq.irq_disable, "cli;", ALT_NOT_XEN);
}

static __always_inline void arch_local_irq_enable(void)
{
        PVOP_ALT_VCALLEE0(irq.irq_enable, "sti;", ALT_NOT_XEN);
}

That very much patches in STI/CLI directly when not Xen.


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