linux-kernel - Re: [PATCH v3] x86/bugs: Only harden syscalls when needed

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Message-ID: <ZiDCz3_0cy1ulw9S@infradead.org>
Date: Wed, 17 Apr 2024 23:50:55 -0700
From: Christoph Hellwig <hch@...radead.org>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexandre Chartre <alexandre.chartre@...cle.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Sean Christopherson <seanjc@...gle.com>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Nikolay Borisov <nik.borisov@...e.com>,
	KP Singh <kpsingh@...nel.org>, Waiman Long <longman@...hat.com>,
	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v3] x86/bugs: Only harden syscalls when needed

On Tue, Apr 16, 2024 at 04:02:21PM -0700, Josh Poimboeuf wrote:
> Syscall hardening (i.e., converting the syscall indirect branch to a
> series of direct branches) may cause performance regressions in certain
> scenarios.

Maybe spell out the scenarios, as this just sounds like hand waiving
right now..