linux-kernel - [RFC PATCH 09/10] x86/fpu: Split out XFEATURE_MASK_KERNEL

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Date:   Fri,  3 Dec 2021 00:36:35 +0000
From:   Jiaxun Yang <jiaxun.yang@...goat.com>
To:     x86@...nel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com,
        chang.seok.bae@...el.com, linux-kernel@...r.kernel.org,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        Jiaxun Yang <j.yang-87@....ed.ac.uk>
Subject: [RFC PATCH 09/10] x86/fpu: Split out XFEATURE_MASK_KERNEL_DYNAMIC

For now, we can have features that is not XFD entitled
dynamically allocated on fxstate buffer.

Split out XFEATURE_MASK_KERNEL_DYNAMIC, and make it depend
on XSAVES (actually XSAVEC but os_xsave only generate
compact format when XSAVES present).

Signed-off-by: Jiaxun Yang <j.yang-87@....ed.ac.uk>
---
 arch/x86/include/asm/fpu/xstate.h | 3 +++
 arch/x86/kernel/fpu/xstate.c      | 3 ++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/fpu/xstate.h b/arch/x86/include/asm/fpu/xstate.h
index c46d3dd591bd..d3a8c0855a5d 100644
--- a/arch/x86/include/asm/fpu/xstate.h
+++ b/arch/x86/include/asm/fpu/xstate.h
@@ -49,6 +49,9 @@
 /* Features which are dynamically enabled for a process on request */
 #define XFEATURE_MASK_USER_DYNAMIC	XFEATURE_MASK_XTILE_DATA
 
+/* Features which are dynamically allocated only when in use */
+#define XFEATURE_MASK_KERNEL_DYNAMIC	XFEATURE_MASK_XTILE_DATA
+
 /* All currently supported supervisor features */
 #define XFEATURE_MASK_SUPERVISOR_SUPPORTED (XFEATURE_MASK_PASID)
 
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 4621b51d1b20..1837e379777f 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -875,7 +875,8 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
 
 	/* Clean out dynamic features from default */
 	fpu_kernel_cfg.default_features = fpu_kernel_cfg.max_features;
-	fpu_kernel_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
+	if (cpu_feature_enabled(X86_FEATURE_XSAVES))
+		fpu_kernel_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
 
 	fpu_user_cfg.default_features = fpu_user_cfg.max_features;
 	fpu_user_cfg.default_features &= ~XFEATURE_MASK_USER_DYNAMIC;
-- 
2.30.2