x86/bugs: Use a static branch to guard IBPB on vCPU switch

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Instead of using X86_FEATURE_USE_IBPB to guard the IBPB execution in KVM
when a new vCPU is loaded, introduce a static branch, similar to
switch_mm_*_ibpb.

This makes it obvious in spectre_v2_user_select_mitigation() what
exactly is being toggled, instead of the unclear X86_FEATURE_USE_IBPB
(which will be shortly removed). It also provides more fine-grained
control, making it simpler to change/add paths that control the IBPB in
the vCPU switch path without affecting other IBPBs.

Signed-off-by: Yosry Ahmed <yosry.ahmed@linux.dev>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@kernel.org>
Acked-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20250227012712.3193063-5-yosry.ahmed@linux.dev

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Yosry Ahmed 2025-02-27 01:27:10 +00:00 • committed by Ingo Molnar

parent bd9a8542ce

commit 80dacb0804

4 changed files with 9 additions and 2 deletions

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2

arch/x86/include/asm/nospec-branch.h

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5

arch/x86/kernel/cpu/bugs.c

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2

arch/x86/kvm/svm/svm.c

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arch/x86/kvm/vmx/vmx.c

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