linux-kernel - [PATCH 05/23] x86/fpu: Add fpu_state_config::legacy

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Date:   Thu, 21 Oct 2021 15:55:09 -0700
From:   "Chang S. Bae" <chang.seok.bae@...el.com>
To:     linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, tglx@...utronix.de, dave.hansen@...ux.intel.com,
        arjan@...ux.intel.com, ravi.v.shankar@...el.com,
        chang.seok.bae@...el.com
Subject: [PATCH 05/23] x86/fpu: Add fpu_state_config::legacy_features

From: Thomas Gleixner <tglx@...utronix.de>

The upcoming prctl() which is required to request the permission for a
dynamically enabled feature will also provide an option to retrieve the
supported features. If the CPU does not support xsave the supported
features would be 0 even when the CPU supports FP and SSE.

Provide separate storage for the legacy feature set to avoid that and fill
in the bits in the legacy init function.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Signed-off-by: Chang S. Bae <chang.seok.bae@...el.com>
---
 arch/x86/include/asm/fpu/types.h | 7 +++++++
 arch/x86/kernel/fpu/init.c       | 9 ++++++---
 2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index d8b59e45dc25..d27ad4842fa1 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -500,6 +500,13 @@ struct fpu_state_config {
 	 * be requested by user space before usage.
 	 */
 	u64 default_features;
+	/*
+	 * @legacy_features:
+	 *
+	 * Features which can be reported back to user space
+	 * even without XSAVE support, i.e. legacy features FP + SSE
+	 */
+	u64 legacy_features;
 };
 
 /* FPU state configuration information */
diff --git a/arch/x86/kernel/fpu/init.c b/arch/x86/kernel/fpu/init.c
index 7074154131e6..621f4b6cac4a 100644
--- a/arch/x86/kernel/fpu/init.c
+++ b/arch/x86/kernel/fpu/init.c
@@ -193,12 +193,15 @@ static void __init fpu__init_system_xstate_size_legacy(void)
 	 * Note that the size configuration might be overwritten later
 	 * during fpu__init_system_xstate().
 	 */
-	if (!cpu_feature_enabled(X86_FEATURE_FPU))
+	if (!cpu_feature_enabled(X86_FEATURE_FPU)) {
 		size = sizeof(struct swregs_state);
-	else if (cpu_feature_enabled(X86_FEATURE_FXSR))
+	} else if (cpu_feature_enabled(X86_FEATURE_FXSR)) {
 		size = sizeof(struct fxregs_state);
-	else
+		fpu_user_cfg.legacy_features = XFEATURE_MASK_FPSSE;
+	} else {
 		size = sizeof(struct fregs_state);
+		fpu_user_cfg.legacy_features = XFEATURE_MASK_FP;
+	}
 
 	fpu_kernel_cfg.max_size = size;
 	fpu_kernel_cfg.default_size = size;
-- 
2.17.1