linux-kernel - [PATCH v5 21/28] x86/fpu/amx: Initialize child's AMX state

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Message-Id: <20210523193259.26200-22-chang.seok.bae@intel.com>
Date:   Sun, 23 May 2021 12:32:52 -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, jing2.liu@...el.com,
        ravi.v.shankar@...el.com, linux-kernel@...r.kernel.org,
        chang.seok.bae@...el.com
Subject: [PATCH v5 21/28] 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 v4:
* Added as a new patch. This was missing on previous versions.
---
 arch/x86/kernel/fpu/core.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
index 016c3adebec3..cccfeafe81e5 100644
--- a/arch/x86/kernel/fpu/core.c
+++ b/arch/x86/kernel/fpu/core.c
@@ -285,6 +285,10 @@ int fpu__copy(struct task_struct *dst, struct task_struct *src)
 
 	fpregs_unlock();
 
+	/* AMX state is volatile, children do not inherit it. */
+	if (xfeatures_mask_all & XFEATURE_MASK_XTILE)
+		dst_fpu->state->xsave.header.xfeatures &= ~(XFEATURE_MASK_XTILE);
+
 	set_tsk_thread_flag(dst, TIF_NEED_FPU_LOAD);
 
 	trace_x86_fpu_copy_src(src_fpu);
-- 
2.17.1