linux-kernel - Re: [PATCH v2] x86/bhi: BHI mitigation can trigger warning in #DB handler

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Message-ID: <20240703062455.ncak7idh2e3fv6sq@treble>
Date: Tue, 2 Jul 2024 23:24:55 -0700
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Alexandre Chartre <alexandre.chartre@...cle.com>
Cc: x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	daniel.sneddon@...ux.intel.com, pawan.kumar.gupta@...ux.intel.com,
	tglx@...utronix.de, konrad.wilk@...cle.com, peterz@...radead.org,
	seanjc@...gle.com, andrew.cooper3@...rix.com,
	dave.hansen@...ux.intel.com, nik.borisov@...e.com,
	kpsingh@...nel.org, longman@...hat.com, bp@...en8.de,
	pbonzini@...hat.com
Subject: Re: [PATCH v2] x86/bhi: BHI mitigation can trigger warning in #DB
 handler

On Fri, May 24, 2024 at 09:04:59AM +0200, Alexandre Chartre wrote:
> When BHI mitigation is enabled, if sysenter is invoked with the TF flag
> set then entry_SYSENTER_compat uses CLEAR_BRANCH_HISTORY and calls the
> clear_bhb_loop() before the TF flag is cleared. This causes the #DB
> handler (exc_debug_kernel) to issue a warning because single-step is
> used outside the entry_SYSENTER_compat function.

Reviewed-by: Josh Poimboeuf <jpoimboe@...nel.org>

-- 
Josh