x86/fpu/xstate: Add helpers for LBR dynamic supervisor feature

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.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Dave Hansen <dave.hansen@intel.com>
Link: https://lkml.kernel.org/r/1593780569-62993-22-git-send-email-kan.liang@linux.intel.com

diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index 040c4d4..c029fce 100644 (file)
--- 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 (file)
--- 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