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    Subject[PATCHv5 06/13] x86/mm: Provide ARCH_GET_UNTAG_MASK and ARCH_ENABLE_TAGGED_ADDR
    Date
    Add a couple of arch_prctl() handles:

    - ARCH_ENABLE_TAGGED_ADDR enabled LAM. The argument is required number
    of tag bits. It is rounded up to the nearest LAM mode that can
    provide it. For now only LAM_U57 is supported, with 6 tag bits.

    - ARCH_GET_UNTAG_MASK returns untag mask. It can indicates where tag
    bits located in the address.

    Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    ---
    arch/x86/include/uapi/asm/prctl.h | 3 ++
    arch/x86/kernel/process_64.c | 60 ++++++++++++++++++++++++++++++-
    2 files changed, 62 insertions(+), 1 deletion(-)

    diff --git a/arch/x86/include/uapi/asm/prctl.h b/arch/x86/include/uapi/asm/prctl.h
    index 500b96e71f18..38164a05c23c 100644
    --- a/arch/x86/include/uapi/asm/prctl.h
    +++ b/arch/x86/include/uapi/asm/prctl.h
    @@ -20,4 +20,7 @@
    #define ARCH_MAP_VDSO_32 0x2002
    #define ARCH_MAP_VDSO_64 0x2003

    +#define ARCH_GET_UNTAG_MASK 0x4001
    +#define ARCH_ENABLE_TAGGED_ADDR 0x4002
    +
    #endif /* _ASM_X86_PRCTL_H */
    diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
    index 1962008fe743..82a19168bfa4 100644
    --- a/arch/x86/kernel/process_64.c
    +++ b/arch/x86/kernel/process_64.c
    @@ -742,6 +742,60 @@ static long prctl_map_vdso(const struct vdso_image *image, unsigned long addr)
    }
    #endif

    +static void enable_lam_func(void *mm)
    +{
    + struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
    + unsigned long lam_mask;
    + unsigned long cr3;
    +
    + if (loaded_mm != mm)
    + return;
    +
    + lam_mask = READ_ONCE(loaded_mm->context.lam_cr3_mask);
    +
    + /* Update CR3 to get LAM active on the CPU */
    + cr3 = __read_cr3();
    + cr3 &= ~(X86_CR3_LAM_U48 | X86_CR3_LAM_U57);
    + cr3 |= lam_mask;
    + write_cr3(cr3);
    + set_tlbstate_cr3_lam_mask(lam_mask);
    +}
    +
    +static int prctl_enable_tagged_addr(struct mm_struct *mm, unsigned long nr_bits)
    +{
    + int ret = 0;
    +
    + if (!cpu_feature_enabled(X86_FEATURE_LAM))
    + return -ENODEV;
    +
    + mutex_lock(&mm->context.lock);
    +
    + /* Already enabled? */
    + if (mm->context.lam_cr3_mask) {
    + ret = -EBUSY;
    + goto out;
    + }
    +
    + if (!nr_bits) {
    + ret = -EINVAL;
    + goto out;
    + } else if (nr_bits <= 6) {
    + mm->context.lam_cr3_mask = X86_CR3_LAM_U57;
    + mm->context.untag_mask = ~GENMASK(62, 57);
    + } else {
    + ret = -EINVAL;
    + goto out;
    + }
    +
    + /* Make lam_cr3_mask and untag_mask visible on other CPUs */
    + smp_mb();
    +
    + on_each_cpu_mask(mm_cpumask(mm), enable_lam_func, mm, true);
    +out:
    + mutex_unlock(&mm->context.lock);
    + return ret;
    +}
    +
    long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
    {
    int ret = 0;
    @@ -829,7 +883,11 @@ long do_arch_prctl_64(struct task_struct *task, int option, unsigned long arg2)
    case ARCH_MAP_VDSO_64:
    return prctl_map_vdso(&vdso_image_64, arg2);
    #endif
    -
    + case ARCH_GET_UNTAG_MASK:
    + return put_user(task->mm->context.untag_mask,
    + (unsigned long __user *)arg2);
    + case ARCH_ENABLE_TAGGED_ADDR:
    + return prctl_enable_tagged_addr(task->mm, arg2);
    default:
    ret = -EINVAL;
    break;
    --
    2.35.1
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