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Message-ID: <20231025150644.xckrfxcr2vxcqvun@desk>
Date: Wed, 25 Oct 2023 08:06:44 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Andy Lutomirski <luto@...nel.org>,
Jonathan Corbet <corbet@....net>,
Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>, tony.luck@...el.com,
ak@...ux.intel.com, tim.c.chen@...ux.intel.com,
linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
kvm@...r.kernel.org,
Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
antonio.gomez.iglesias@...ux.intel.com,
Alyssa Milburn <alyssa.milburn@...el.com>
Subject: Re: [PATCH v2 1/6] x86/bugs: Add asm helpers for executing VERW
On Wed, Oct 25, 2023 at 08:56:10AM +0200, Peter Zijlstra wrote:
> > config3: 32-bit mode, pre-boot objdump
> >
> > entry_SYSENTER_32:
> > ...
> > c8e: 58 pop %eax
> > c8f: 90 nop
> > c90: 90 nop
> > c91: 90 nop
> > c92: 90 nop
> > c93: 90 nop
> > c94: 90 nop
> > c95: 90 nop
> > c96: fb sti
> > c97: 0f 35 sysexit
> >
>
> If you look at arch/x86/include/asm/nops.h, you'll find (for 32bit):
>
> * 7: leal 0x0(%esi,%eiz,1),%esi
>
> Which reads as:
>
> load-effective-address of %esi[0] into %esi
Wow, never imagined that this would be one of the magician's trick. I
will go read on why is it better than NOPL.
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