linux-kernel - Re: [PATCH v4] x86/entry_32: Use stack segment selector for VERW operand

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Message-ID: <20240711183410.zakyzfpfy6p7komx@desk>
Date: Thu, 11 Jul 2024 11:34:10 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Jiri Slaby <jirislaby@...nel.org>
Cc: Uros Bizjak <ubizjak@...il.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	Robert Gill <rtgill82@...il.com>,
	Jari Ruusu <jariruusu@...tonmail.com>,
	Brian Gerst <brgerst@...il.com>,
	"Linux regression tracking (Thorsten Leemhuis)" <regressions@...mhuis.info>,
	antonio.gomez.iglesias@...ux.intel.com,
	daniel.sneddon@...ux.intel.com, stable@...r.kernel.org
Subject: Re: [PATCH v4] x86/entry_32: Use stack segment selector for VERW
 operand

On Thu, Jul 11, 2024 at 07:49:25AM +0200, Jiri Slaby wrote:
> > > Why not simply:
> > > 
> > > .macro CLEAR_CPU_BUFFERS_SAFE
> > > 	ALTERNATIVE "", __stringify(verw %ss:_ASM_RIP(mds_verw_sel)),
> > > X86_FEATURE_CLEAR_CPU_BUF
> > > .endm
> > 
> > We can do it this way as well. But, there are stable kernels that don't
> > support relocations in ALTERNATIVEs. The way it is done in current patch
> > can be backported without worrying about which kernels support relocations.
> 
> This sounds weird. There are code bases without ALTERNATIVE support at all.
> Will you expand ALTERNATIVE into some cmp & jmp here due to that? No.

Agree, will change it to the way Uros and Peter suggested.

> Instead, you can send this "backport" to stable for older kernels later,
> once a proper patch is merged.

Ok, will take care of the differences in the backports.