linux-kernel - Re: [PATCH v1 2/2] perf/x86/kvm: Avoid unnecessary work in guest filtering

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Message-ID: <alpine.DEB.2.21.1810061632100.5454@nanos.tec.linutronix.de>
Date:   Sat, 6 Oct 2018 16:40:53 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andi Kleen <andi@...stfloor.org>
cc:     peterz@...radead.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        eranian@...gle.com, kan.liang@...el.com, isaku.yamahata@...el.com,
        kvm@...r.kernel.org, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v1 2/2] perf/x86/kvm: Avoid unnecessary work in guest
 filtering

On Fri, 5 Oct 2018, Andi Kleen wrote:
> Some time ago KVM added a workaround for PEBS events leaking
> into guests. This uses the KVM entry/exit list to add an extra
> disable of the PEBS_ENABLE MSR.
> 
> Intel also added a fix for this issue to microcode updates on
> Haswell/Broadwell/Skylake.
> 
> It turns out using the MSR entry/exit list makes VM exits
> significantly slower. The list is only needed for disabling
> PEBS, because the GLOBAL_CTRL change gets optimized by
> KVM into changing the VMCS.
> 
> This patch checks for the microcode updates that have the microcode

# grep "This patch" Documentation/process

> fix for leaking PEBS, and disables the extra entry/exit list
> entry for PEBS_ENABLE. In addition we always clear the
> GLOBAL_CTRL for the PEBS counter while running in the guest,
> which is enough to make them never fire at the wrong
> side of the host/guest transition.
>  
> +#define IUCODE(model, step, rev) \
> +	{ X86_VENDOR_INTEL, 6, model, step, rev, 0, 0 }

So we are going to have this kind of defines on every usage site. Please
put these macros into the corresponding header file.

Also this wants to be named INTEL_MIN_UCODE() so it's clear what this is
about.

Thanks,

	tglx