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    Subject[PATCH 5.10 109/130] x86/bugs: Do IBPB fallback check only once
    Date
    From: Josh Poimboeuf <jpoimboe@kernel.org>

    commit 0fe4aeea9c01baabecc8c3afc7889c809d939bc2 upstream.

    When booting with retbleed=auto, if the kernel wasn't built with
    CONFIG_CC_HAS_RETURN_THUNK, the mitigation falls back to IBPB. Make
    sure a warning is printed in that case. The IBPB fallback check is done
    twice, but it really only needs to be done once.

    Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/kernel/cpu/bugs.c | 15 +++++----------
    1 file changed, 5 insertions(+), 10 deletions(-)

    --- a/arch/x86/kernel/cpu/bugs.c
    +++ b/arch/x86/kernel/cpu/bugs.c
    @@ -847,18 +847,13 @@ static void __init retbleed_select_mitig
    case RETBLEED_CMD_AUTO:
    default:
    if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
    - boot_cpu_data.x86_vendor == X86_VENDOR_HYGON) {
    -
    - if (IS_ENABLED(CONFIG_RETPOLINE) &&
    - IS_ENABLED(CONFIG_CC_HAS_RETURN_THUNK))
    - retbleed_mitigation = RETBLEED_MITIGATION_UNRET;
    - else
    - retbleed_mitigation = RETBLEED_MITIGATION_IBPB;
    - }
    + boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
    + retbleed_mitigation = RETBLEED_MITIGATION_UNRET;

    /*
    - * The Intel mitigation (IBRS) was already selected in
    - * spectre_v2_select_mitigation().
    + * The Intel mitigation (IBRS or eIBRS) was already selected in
    + * spectre_v2_select_mitigation(). 'retbleed_mitigation' will
    + * be set accordingly below.
    */

    break;

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