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    Subject[PATCH 5.15 45/89] x86/bugs: Keep a per-CPU IA32_SPEC_CTRL value
    Date
    From: Peter Zijlstra <peterz@infradead.org>

    commit caa0ff24d5d0e02abce5e65c3d2b7f20a6617be5 upstream.

    Due to TIF_SSBD and TIF_SPEC_IB the actual IA32_SPEC_CTRL value can
    differ from x86_spec_ctrl_base. As such, keep a per-CPU value
    reflecting the current task's MSR content.

    [jpoimboe: rename]

    Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
    Signed-off-by: Borislav Petkov <bp@suse.de>
    Reviewed-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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    arch/x86/include/asm/nospec-branch.h | 1 +
    arch/x86/kernel/cpu/bugs.c | 28 +++++++++++++++++++++++-----
    arch/x86/kernel/process.c | 2 +-
    3 files changed, 25 insertions(+), 6 deletions(-)

    --- a/arch/x86/include/asm/nospec-branch.h
    +++ b/arch/x86/include/asm/nospec-branch.h
    @@ -254,6 +254,7 @@ static inline void indirect_branch_predi

    /* The Intel SPEC CTRL MSR base value cache */
    extern u64 x86_spec_ctrl_base;
    +extern void write_spec_ctrl_current(u64 val);

    /*
    * With retpoline, we must use IBRS to restrict branch prediction
    --- a/arch/x86/kernel/cpu/bugs.c
    +++ b/arch/x86/kernel/cpu/bugs.c
    @@ -49,12 +49,30 @@ static void __init mmio_select_mitigatio
    static void __init srbds_select_mitigation(void);
    static void __init l1d_flush_select_mitigation(void);

    -/* The base value of the SPEC_CTRL MSR that always has to be preserved. */
    +/* The base value of the SPEC_CTRL MSR without task-specific bits set */
    u64 x86_spec_ctrl_base;
    EXPORT_SYMBOL_GPL(x86_spec_ctrl_base);
    +
    +/* The current value of the SPEC_CTRL MSR with task-specific bits set */
    +DEFINE_PER_CPU(u64, x86_spec_ctrl_current);
    +EXPORT_SYMBOL_GPL(x86_spec_ctrl_current);
    +
    static DEFINE_MUTEX(spec_ctrl_mutex);

    /*
    + * Keep track of the SPEC_CTRL MSR value for the current task, which may differ
    + * from x86_spec_ctrl_base due to STIBP/SSB in __speculation_ctrl_update().
    + */
    +void write_spec_ctrl_current(u64 val)
    +{
    + if (this_cpu_read(x86_spec_ctrl_current) == val)
    + return;
    +
    + this_cpu_write(x86_spec_ctrl_current, val);
    + wrmsrl(MSR_IA32_SPEC_CTRL, val);
    +}
    +
    +/*
    * The vendor and possibly platform specific bits which can be modified in
    * x86_spec_ctrl_base.
    */
    @@ -1272,7 +1290,7 @@ static void __init spectre_v2_select_mit
    if (spectre_v2_in_eibrs_mode(mode)) {
    /* Force it so VMEXIT will restore correctly */
    x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
    - wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
    + write_spec_ctrl_current(x86_spec_ctrl_base);
    }

    switch (mode) {
    @@ -1327,7 +1345,7 @@ static void __init spectre_v2_select_mit

    static void update_stibp_msr(void * __unused)
    {
    - wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
    + write_spec_ctrl_current(x86_spec_ctrl_base);
    }

    /* Update x86_spec_ctrl_base in case SMT state changed. */
    @@ -1570,7 +1588,7 @@ static enum ssb_mitigation __init __ssb_
    x86_amd_ssb_disable();
    } else {
    x86_spec_ctrl_base |= SPEC_CTRL_SSBD;
    - wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
    + write_spec_ctrl_current(x86_spec_ctrl_base);
    }
    }

    @@ -1821,7 +1839,7 @@ int arch_prctl_spec_ctrl_get(struct task
    void x86_spec_ctrl_setup_ap(void)
    {
    if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
    - wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
    + write_spec_ctrl_current(x86_spec_ctrl_base);

    if (ssb_mode == SPEC_STORE_BYPASS_DISABLE)
    x86_amd_ssb_disable();
    --- a/arch/x86/kernel/process.c
    +++ b/arch/x86/kernel/process.c
    @@ -584,7 +584,7 @@ static __always_inline void __speculatio
    }

    if (updmsr)
    - wrmsrl(MSR_IA32_SPEC_CTRL, msr);
    + write_spec_ctrl_current(msr);
    }

    static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)

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