linux-kernel - [PATCH v8 20/26] x86/fpu/amx: Initialize child's AMX state

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Message-Id: <20210717152903.7651-21-chang.seok.bae@intel.com>
Date:   Sat, 17 Jul 2021 08:28:57 -0700
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     bp@...e.de, luto@...nel.org, tglx@...utronix.de, mingo@...nel.org,
        x86@...nel.org
Cc:     len.brown@...el.com, dave.hansen@...el.com,
        thiago.macieira@...el.com, jing2.liu@...el.com,
        ravi.v.shankar@...el.com, linux-kernel@...r.kernel.org,
        chang.seok.bae@...el.com
Subject: [PATCH v8 20/26] x86/fpu/amx: Initialize child's AMX state

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

Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
Reviewed-by: Len Brown <len.brown@...el.com>
Cc: x86@...nel.org
Cc: linux-kernel@...r.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 907f11f95330..80bf107d515c 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