[tip: x86/fpu] x86/fpu: Add basic helpers for dynamically enabled features

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the x86/fpu branch of tip:

Commit-ID:     23686ef25d4ae81bc12fe3994d1905191fcf71f8
Gitweb:        https://git.kernel.org/tip/23686ef25d4ae81bc12fe3994d1905191fcf71f8
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Thu, 21 Oct 2021 15:55:11 -07:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 26 Oct 2021 10:18:09 +02:00

x86/fpu: Add basic helpers for dynamically enabled features

To allow building up the infrastructure required to support dynamically
enabled FPU features, add:

 - XFEATURES_MASK_DYNAMIC

   This constant will hold xfeatures which can be dynamically enabled.

 - fpu_state_size_dynamic()

   A static branch for 64-bit and a simple 'return false' for 32-bit.

   This helper allows to add dynamic-feature-specific changes to common
   code which is shared between 32-bit and 64-bit without #ifdeffery.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/20211021225527.10184-8-chang.seok.bae@xxxxxxxxx
---
 arch/x86/include/asm/fpu/xstate.h | 21 +++++++++++++++++++++
 arch/x86/kernel/fpu/core.c        |  4 ++++
 2 files changed, 25 insertions(+)

diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index 43ae89d..cf28546 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -43,6 +43,9 @@
 #define XFEATURE_MASK_USER_RESTORE	\
 	(XFEATURE_MASK_USER_SUPPORTED & ~XFEATURE_MASK_PKRU)
 
+/* Features which are dynamically enabled for a process on request */
+#define XFEATURE_MASK_USER_DYNAMIC	0ULL
+
 /* All currently supported supervisor features */
 #define XFEATURE_MASK_SUPERVISOR_SUPPORTED (XFEATURE_MASK_PASID)
 
@@ -96,4 +99,22 @@ int xfeature_size(int xfeature_nr);
 void xsaves(struct xregs_state *xsave, u64 mask);
 void xrstors(struct xregs_state *xsave, u64 mask);
 
+#ifdef CONFIG_X86_64
+DECLARE_STATIC_KEY_FALSE(__fpu_state_size_dynamic);
+#endif
+
+#ifdef CONFIG_X86_64
+DECLARE_STATIC_KEY_FALSE(__fpu_state_size_dynamic);
+
+static __always_inline __pure bool fpu_state_size_dynamic(void)
+{
+	return static_branch_unlikely(&__fpu_state_size_dynamic);
+}
+#else
+static __always_inline __pure bool fpu_state_size_dynamic(void)
+{
+	return false;
+}
+#endif
+
 #endif
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index b05f6a3..4018083 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -25,6 +25,10 @@
 #define CREATE_TRACE_POINTS
 #include <asm/trace/fpu.h>
 
+#ifdef CONFIG_X86_64
+DEFINE_STATIC_KEY_FALSE(__fpu_state_size_dynamic);
+#endif
+
 /* The FPU state configuration data for kernel and user space */
 struct fpu_state_config	fpu_kernel_cfg __ro_after_init;
 struct fpu_state_config fpu_user_cfg __ro_after_init;