linux-kernel - Re: [PATCH v6 7/9] x86/vmscape: Deploy BHB clearing mitigation

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Message-ID: <fbe2eaba-811c-465e-9d99-20d0f0fd3d97@suse.com>
Date: Thu, 11 Dec 2025 16:26:27 +0200
From: Nikolay Borisov <nik.borisov@...e.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>, x86@...nel.org,
 David Kaplan <david.kaplan@....com>, "H. Peter Anvin" <hpa@...or.com>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Sean Christopherson
 <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
 Asit Mallick <asit.k.mallick@...el.com>, Tao Zhang <tao1.zhang@...el.com>
Subject: Re: [PATCH v6 7/9] x86/vmscape: Deploy BHB clearing mitigation

On 2.12.25 г. 8:20 ч., Pawan Gupta wrote:
> IBPB mitigation for VMSCAPE is an overkill on CPUs that are only affected
> by the BHI variant of VMSCAPE. On such CPUs, eIBRS already provides
> indirect branch isolation between guest and host userspace. However, branch
> history from guest may also influence the indirect branches in host
> userspace.
> 
> To mitigate the BHI aspect, use clear_bhb_loop().
> 
> Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>

Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>