[PATCH v9 20/26] x86/fpu/amx: Initialize child's AMX state

Chang S. Bae
2021-07-30T15:07:14Z

Assure that a forked child starts AMX registers in the INIT-state.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Reviewed-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
---
Changes from v5:
* Introduced a new define. (Andy Lutomirski)

Changes from v4:
* Added as a new patch. This was missing on previous versions.
---
arch/x86/include/asm/fpu/xstate.h | 3 +++
arch/x86/kernel/fpu/core.c | 3 +++
2 files changed, 6 insertions(+)

diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index e7c6396261ca..912b420cb148 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -80,6 +80,9 @@
XFEATURE_MASK_INDEPENDENT | \
XFEATURE_MASK_SUPERVISOR_UNSUPPORTED)

+/* Volatile states that a child does not inherit. */
+#define XFEATURE_MASK_CLEARED_ON_CLONE XFEATURE_MASK_XTILE
+
#ifdef CONFIG_X86_64
#define REX_PREFIX "0x48, "
#else
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 541628bfc8c0..387118127f93 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -299,6 +299,9 @@ int fpu_clone(struct task_struct *dst)
save_fpregs_to_fpstate(dst_fpu);
fpregs_unlock();

+ if (xfeatures_mask_all & XFEATURE_MASK_CLEARED_ON_CLONE)
+ dst_fpu->state->xsave.header.xfeatures &= ~XFEATURE_MASK_CLEARED_ON_CLONE;
+
set_tsk_thread_flag(dst, TIF_NEED_FPU_LOAD);

trace_x86_fpu_copy_src(src_fpu);
--
2.17.1