This is a note to let you know that I've just added the patch titled arm64: errata: Fix KVM Spectre-v2 mitigation selection for Cortex-A57/A72 to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: arm64-errata-fix-kvm-spectre-v2-mitigation-selection-for-cortex-a57-a72.patch and it can be found in the queue-4.9 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From foo@baz Sat Dec 3 02:32:26 PM CET 2022 From: James Morse <james.morse@xxxxxxx> Date: Wed, 30 Nov 2022 18:29:56 +0000 Subject: arm64: errata: Fix KVM Spectre-v2 mitigation selection for Cortex-A57/A72 To: stable@xxxxxxxxxxxxxxx, linux-arm-kernel@xxxxxxxxxxxxxxxxxxx Cc: Catalin Marinas <catalin.marinas@xxxxxxx>, James Morse <james.morse@xxxxxxx> Message-ID: <20221130182956.739350-3-james.morse@xxxxxxx> From: James Morse <james.morse@xxxxxxx> Both the Spectre-v2 and Spectre-BHB mitigations involve running a sequence immediately after exiting a guest, before any branches. In the stable kernels these sequences are built by copying templates into an empty vector slot. For Spectre-BHB, Cortex-A57 and A72 require the branchy loop with k=8. If Spectre-v2 needs mitigating at the same time, a firmware call to EL3 is needed. The work EL3 does at this point is also enough to mitigate Spectre-BHB. When enabling the Spectre-BHB mitigation, spectre_bhb_enable_mitigation() should check if a slot has already been allocated for Spectre-v2, meaning no work is needed for Spectre-BHB. This check was missed in the earlier backport, add it. Fixes: 4dd8aae585a5 ("arm64: Mitigate spectre style branch history side channels") Signed-off-by: James Morse <james.morse@xxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- arch/arm64/kernel/cpu_errata.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) --- a/arch/arm64/kernel/cpu_errata.c +++ b/arch/arm64/kernel/cpu_errata.c @@ -876,7 +876,13 @@ void spectre_bhb_enable_mitigation(const } else if (spectre_bhb_loop_affected(SCOPE_LOCAL_CPU)) { switch (spectre_bhb_loop_affected(SCOPE_SYSTEM)) { case 8: - kvm_setup_bhb_slot(__spectre_bhb_loop_k8_start); + /* + * A57/A72-r0 will already have selected the + * spectre-indirect vector, which is sufficient + * for BHB too. + */ + if (!__this_cpu_read(bp_hardening_data.fn)) + kvm_setup_bhb_slot(__spectre_bhb_loop_k8_start); break; case 24: kvm_setup_bhb_slot(__spectre_bhb_loop_k24_start); Patches currently in stable-queue which might be from james.morse@xxxxxxx are queue-4.9/arm64-errata-fix-kvm-spectre-v2-mitigation-selection-for-cortex-a57-a72.patch queue-4.9/arm64-fix-panic-when-spectre-v2-causes-spectre-bhb-to-re-allocate-kvm-vectors.patch