linux-kernel - Re: [PATCH v6 0/5] x86: Enable LKGS instruction

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Date:   Fri, 13 Jan 2023 14:29:30 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Xin Li <xin3.li@...el.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, brgerst@...il.com,
        chang.seok.bae@...el.com, jgross@...e.com
Subject: Re: [PATCH v6 0/5] x86: Enable LKGS instruction


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Thu, Jan 12, 2023 at 01:13:20PM +0100, Ingo Molnar wrote:
> > 
> > * Xin Li <xin3.li@...el.com> wrote:
> > 
> > > LKGS instruction is introduced with Intel FRED (flexible return and 
> > > event delivery) specification. As LKGS is independent of FRED, we 
> > > enable it as a standalone CPU feature.
> > > 
> > > LKGS behaves like the MOV to GS instruction except that it loads the 
> > > base address into the IA32_KERNEL_GS_BASE MSR instead of the GS 
> > > segment’s descriptor cache, which is exactly what Linux kernel does 
> > > to load user level GS base.  Thus, with LKGS, there is no need to 
> > > SWAPGS away from the kernel GS base.
> > 
> > Ok, this looks good to me.
> > 
> > I've applied the first 4 patches to tip:x86/cpu, as the instruction 
> > exists in a public document and these patches are fine stand-alone as 
> > well, such as the factoring out of load_gs_index() methods from a 
> > high-use low level header into a new header file.
> > 
> > Planning to apply the final, LKGS enabler patch as well, unless there's 
> > any objections from others?
> 
> Nah, I think that thing's bike-shedded to near death. Let's just do it.

Ok - applied the #5 patch to tip:x86/cpu, for a v6.3 merge.

Thanks,

	Ingo