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    Subject[PATCH V2 21/23] x86/fpu/xstate: Add helpers for LBR dynamic supervisor feature
    Date
    From: Kan Liang <kan.liang@linux.intel.com>

    The perf subsystem will only need to save/restore the LBR state.
    However, the existing helpers save all supported supervisor states to a
    kernel buffer, which will be unnecessary. Two helpers are introduced to
    only save/restore requested dynamic supervisor states. The supervisor
    features in XFEATURE_MASK_SUPERVISOR_SUPPORTED and
    XFEATURE_MASK_SUPERVISOR_UNSUPPORTED mask cannot be saved/restored using
    these helpers.

    The helpers will be used in the following patch.

    Reviewed-by: Dave Hansen <dave.hansen@intel.com>
    Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
    ---
    arch/x86/include/asm/fpu/xstate.h | 3 ++
    arch/x86/kernel/fpu/xstate.c | 72 +++++++++++++++++++++++++++++++++++++++
    2 files changed, 75 insertions(+)

    diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
    index 040c4d4..c029fce 100644
    --- a/arch/x86/include/asm/fpu/xstate.h
    +++ b/arch/x86/include/asm/fpu/xstate.h
    @@ -106,6 +106,9 @@ int copy_xstate_to_user(void __user *ubuf, struct xregs_state *xsave, unsigned i
    int copy_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf);
    int copy_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf);
    void copy_supervisor_to_kernel(struct xregs_state *xsave);
    +void copy_dynamic_supervisor_to_kernel(struct xregs_state *xstate, u64 mask);
    +void copy_kernel_to_dynamic_supervisor(struct xregs_state *xstate, u64 mask);
    +

    /* Validate an xstate header supplied by userspace (ptrace or sigreturn) */
    int validate_user_xstate_header(const struct xstate_header *hdr);
    diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
    index dcf0624..b0c22b7 100644
    --- a/arch/x86/kernel/fpu/xstate.c
    +++ b/arch/x86/kernel/fpu/xstate.c
    @@ -1361,6 +1361,78 @@ void copy_supervisor_to_kernel(struct xregs_state *xstate)
    }
    }

    +/**
    + * copy_dynamic_supervisor_to_kernel() - Save dynamic supervisor states to
    + * an xsave area
    + * @xstate: A pointer to an xsave area
    + * @mask: Represent the dynamic supervisor features saved into the xsave area
    + *
    + * Only the dynamic supervisor states sets in the mask are saved into the xsave
    + * area (See the comment in XFEATURE_MASK_DYNAMIC for the details of dynamic
    + * supervisor feature). Besides the dynamic supervisor states, the legacy
    + * region and XSAVE header are also saved into the xsave area. The supervisor
    + * features in the XFEATURE_MASK_SUPERVISOR_SUPPORTED and
    + * XFEATURE_MASK_SUPERVISOR_UNSUPPORTED are not saved.
    + *
    + * The xsave area must be 64-bytes aligned.
    + */
    +void copy_dynamic_supervisor_to_kernel(struct xregs_state *xstate, u64 mask)
    +{
    + u64 dynamic_mask = xfeatures_mask_dynamic() & mask;
    + u32 lmask, hmask;
    + int err;
    +
    + if (WARN_ON_FPU(!boot_cpu_has(X86_FEATURE_XSAVES)))
    + return;
    +
    + if (WARN_ON_FPU(!dynamic_mask))
    + return;
    +
    + lmask = dynamic_mask;
    + hmask = dynamic_mask >> 32;
    +
    + XSTATE_OP(XSAVES, xstate, lmask, hmask, err);
    +
    + /* Should never fault when copying to a kernel buffer */
    + WARN_ON_FPU(err);
    +}
    +
    +/**
    + * copy_kernel_to_dynamic_supervisor() - Restore dynamic supervisor states from
    + * an xsave area
    + * @xstate: A pointer to an xsave area
    + * @mask: Represent the dynamic supervisor features restored from the xsave area
    + *
    + * Only the dynamic supervisor states sets in the mask are restored from the
    + * xsave area (See the comment in XFEATURE_MASK_DYNAMIC for the details of
    + * dynamic supervisor feature). Besides the dynamic supervisor states, the
    + * legacy region and XSAVE header are also restored from the xsave area. The
    + * supervisor features in the XFEATURE_MASK_SUPERVISOR_SUPPORTED and
    + * XFEATURE_MASK_SUPERVISOR_UNSUPPORTED are not restored.
    + *
    + * The xsave area must be 64-bytes aligned.
    + */
    +void copy_kernel_to_dynamic_supervisor(struct xregs_state *xstate, u64 mask)
    +{
    + u64 dynamic_mask = xfeatures_mask_dynamic() & mask;
    + u32 lmask, hmask;
    + int err;
    +
    + if (WARN_ON_FPU(!boot_cpu_has(X86_FEATURE_XSAVES)))
    + return;
    +
    + if (WARN_ON_FPU(!dynamic_mask))
    + return;
    +
    + lmask = dynamic_mask;
    + hmask = dynamic_mask >> 32;
    +
    + XSTATE_OP(XRSTORS, xstate, lmask, hmask, err);
    +
    + /* Should never fault when copying from a kernel buffer */
    + WARN_ON_FPU(err);
    +}
    +
    #ifdef CONFIG_PROC_PID_ARCH_STATUS
    /*
    * Report the amount of time elapsed in millisecond since last AVX512
    --
    2.7.4
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