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    Subject[PATCH 5.10 115/130] x86/speculation: Use cached host SPEC_CTRL value for guest entry/exit
    Date
    From: Josh Poimboeuf <jpoimboe@kernel.org>

    commit bbb69e8bee1bd882784947095ffb2bfe0f7c9470 upstream.

    There's no need to recalculate the host value for every entry/exit.
    Just use the cached value in spec_ctrl_current().

    Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.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 | 12 +-----------
    1 file changed, 1 insertion(+), 11 deletions(-)

    --- a/arch/x86/kernel/cpu/bugs.c
    +++ b/arch/x86/kernel/cpu/bugs.c
    @@ -199,7 +199,7 @@ void __init check_bugs(void)
    void
    x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
    {
    - u64 msrval, guestval, hostval = x86_spec_ctrl_base;
    + u64 msrval, guestval, hostval = spec_ctrl_current();
    struct thread_info *ti = current_thread_info();

    /* Is MSR_SPEC_CTRL implemented ? */
    @@ -212,15 +212,6 @@ x86_virt_spec_ctrl(u64 guest_spec_ctrl,
    guestval = hostval & ~x86_spec_ctrl_mask;
    guestval |= guest_spec_ctrl & x86_spec_ctrl_mask;

    - /* SSBD controlled in MSR_SPEC_CTRL */
    - if (static_cpu_has(X86_FEATURE_SPEC_CTRL_SSBD) ||
    - static_cpu_has(X86_FEATURE_AMD_SSBD))
    - hostval |= ssbd_tif_to_spec_ctrl(ti->flags);
    -
    - /* Conditional STIBP enabled? */
    - if (static_branch_unlikely(&switch_to_cond_stibp))
    - hostval |= stibp_tif_to_spec_ctrl(ti->flags);
    -
    if (hostval != guestval) {
    msrval = setguest ? guestval : hostval;
    wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
    @@ -1353,7 +1344,6 @@ static void __init spectre_v2_select_mit
    pr_err(SPECTRE_V2_EIBRS_EBPF_MSG);

    if (spectre_v2_in_ibrs_mode(mode)) {
    - /* Force it so VMEXIT will restore correctly */
    x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
    write_spec_ctrl_current(x86_spec_ctrl_base, true);
    }

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