[PATCH v7 20/26] x86/fpu/amx: Initialize child's AMX state

From: "Chang S. Bae" <chang.seok.bae@intel.com>
To: bp@suse.de, luto@kernel.org, tglx@linutronix.de,
	mingo@kernel.org, x86@kernel.org
Cc: len.brown@intel.com, dave.hansen@intel.com,
	thiago.macieira@intel.com, jing2.liu@intel.com,
	ravi.v.shankar@intel.com, linux-kernel@vger.kernel.org,
	chang.seok.bae@intel.com
Subject: [PATCH v7 20/26] x86/fpu/amx: Initialize child's AMX state
Date: Sat, 10 Jul 2021 06:03:07 -0700	[thread overview]
Message-ID: <20210710130313.5072-21-chang.seok.bae@intel.com> (raw)
In-Reply-To: <20210710130313.5072-1-chang.seok.bae@intel.com>

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 dbf0db1df9bf..bd7df0e7fc2b 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 ed127c4d182b..e8912b5b9369 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

