linux-kernel - [PATCH 0/2] KVM: x86: Plug an intra-guest Spectre v2 hole

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Message-ID: <20260128013432.3250805-1-seanjc@google.com>
Date: Tue, 27 Jan 2026 17:34:30 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Yosry Ahmed <yosry.ahmed@...ux.dev>, Jim Mattson <jmattson@...gle.com>, 
	David Kaplan <david.kaplan@....com>
Subject: [PATCH 0/2] KVM: x86: Plug an intra-guest Spectre v2 hole

Fix a bug where KVM neglects to emit IBPB when a vCPU is migrated *back* to
a previous pCPU, in which case a misbehaving task B in the guest can unduly
infuence e.g. the BTB of task A in the guest (running in the same vCPU).

FWIW, I've had the first patch sitting around for several months as a
micro-optimization, but was never posted it as I wasn't 100% confident my
analysis was correct.  But it makes plugging this hole much easier, so here
it is...  Reviews most definitely welcome.

Sean Christopherson (2):
  KVM: x86: Defer IBPBs for vCPU and nested transitions until core run
    loop
  KVM: x86: Emit IBPB on pCPU migration if IBPB is advertised to guest

 arch/x86/include/asm/kvm_host.h |  1 +
 arch/x86/kvm/x86.c              | 20 +++++++++++++++++++-
 arch/x86/kvm/x86.h              |  2 +-
 3 files changed, 21 insertions(+), 2 deletions(-)

base-commit: e81f7c908e1664233974b9f20beead78cde6343a
-- 
2.52.0.457.g6b5491de43-goog