linux-kernel - Re: [PATCH v3 3/4] Revert "x86/retpoline: Simplify vmexit_fill

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Date:   Tue, 20 Feb 2018 09:35:25 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     David Woodhouse <dwmw@...zon.co.uk>
cc:     karahmed@...zon.de, x86@...nel.org, kvm@...r.kernel.org,
        torvalds@...ux-foundation.org, pbonzini@...hat.com,
        linux-kernel@...r.kernel.org, bp@...en8.de, peterz@...radead.org,
        jmattson@...gle.com, rkrcmar@...hat.com,
        arjan.van.de.ven@...el.com, dave.hansen@...el.com, mingo@...nel.org
Subject: Re: [PATCH v3 3/4] Revert "x86/retpoline: Simplify
 vmexit_fill_RSB()"

On Mon, 19 Feb 2018, David Woodhouse wrote:

> This reverts commit 1dde7415e99933bb7293d6b2843752cbdb43ec11. By putting
> the RSB filling out of line and calling it, we waste one RSB slot for
> returning from the function itself, which means one fewer actual function
> call we can make if we're doing the Skylake abomination of call-depth
> counting.
> 
> It also changed the number of RSB stuffings we do on vmexit from 32,
> which was correct, to 16. Let's just stop with the bikeshedding; it
> didn't actually *fix* anything anyway.
> 
> Signed-off-by: David Woodhouse <dwmw@...zon.co.uk>

Acked-by: Thomas Gleixner <tglx@...utronix.de>