linux-kernel - Re: [PATCH v3 4/6] x86/gsseg: move local_irq_save/restore() into asm_load_gs

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Date:   Sat, 15 Oct 2022 10:51:54 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Xin Li <xin3.li@...el.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Cc:     mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, peterz@...radead.org, brgerst@...il.com,
        chang.seok.bae@...el.com
Subject: Re: [PATCH v3 4/6] x86/gsseg: move local_irq_save/restore() into
 asm_load_gs_index()

On Thu, Oct 13 2022 at 13:01, Xin Li wrote:
> From: "H. Peter Anvin (Intel)" <hpa@...or.com>
>
> The need to disable/enable interrupts around asm_load_gs_index() is a
> consequence of the implementation. Prepare for using the LKGS
> instruction, which is locally atomic and therefore doesn't need
> interrupts disabled.

*Shudder*. We want less ASM not more.

>  static inline void native_load_gs_index(unsigned int selector)
>  {
> -	unsigned long flags;
> -
> -	local_irq_save(flags);
>  	asm_load_gs_index(selector);
> -	local_irq_restore(flags);
>  }

static inline void native_load_gs_index(unsigned int selector)
{
	unsigned long flags;

        if (cpu_feature_enabled(LKGS)) {
              native_lkgs(selector);
        } else {
	      local_irq_save(flags);
              asm_load_gs_index(selector);
	      local_irq_restore(flags);
       }
}

For paravirt enabled kernels we want during feature detection:

        if (cpu_feature_enabled(LKGS)))
        	pv_ops.cpu.load_gs_index = native_lkgs;

No?

Thanks,

        tglx