linux-kernel - [tip: x86/urgent] x86/fpu: Set X86_FEATURE_OSXSAVE feature after enabling OSXSAVE in CR4

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Message-ID: <169286827486.27769.994183123873151501.tip-bot2@tip-bot2>
Date:   Thu, 24 Aug 2023 09:11:14 -0000
From:   "tip-bot2 for Feng Tang" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     kernel test robot <oliver.sang@...el.com>,
        Feng Tang <feng.tang@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>, stable@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/fpu: Set X86_FEATURE_OSXSAVE feature after
 enabling OSXSAVE in CR4

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     2c66ca3949dc701da7f4c9407f2140ae425683a5
Gitweb:        https://git.kernel.org/tip/2c66ca3949dc701da7f4c9407f2140ae425683a5
Author:        Feng Tang <feng.tang@...el.com>
AuthorDate:    Wed, 23 Aug 2023 14:57:47 +08:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Thu, 24 Aug 2023 11:01:45 +02:00

x86/fpu: Set X86_FEATURE_OSXSAVE feature after enabling OSXSAVE in CR4

0-Day found a 34.6% regression in stress-ng's 'af-alg' test case, and
bisected it to commit b81fac906a8f ("x86/fpu: Move FPU initialization into
arch_cpu_finalize_init()"), which optimizes the FPU init order, and moves
the CR4_OSXSAVE enabling into a later place:

   arch_cpu_finalize_init
       identify_boot_cpu
	   identify_cpu
	       generic_identify
                   get_cpu_cap --> setup cpu capability
       ...
       fpu__init_cpu
           fpu__init_cpu_xstate
               cr4_set_bits(X86_CR4_OSXSAVE);

As the FPU is not yet initialized the CPU capability setup fails to set
X86_FEATURE_OSXSAVE. Many security module like 'camellia_aesni_avx_x86_64'
depend on this feature and therefore fail to load, causing the regression.

Cure this by setting X86_FEATURE_OSXSAVE feature right after OSXSAVE
enabling.

[ tglx: Moved it into the actual BSP FPU initialization code and added a comment ]

Fixes: b81fac906a8f ("x86/fpu: Move FPU initialization into arch_cpu_finalize_init()")
Reported-by: kernel test robot <oliver.sang@...el.com>
Signed-off-by: Feng Tang <feng.tang@...el.com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/lkml/202307192135.203ac24e-oliver.sang@intel.com
Link: https://lore.kernel.org/lkml/20230823065747.92257-1-feng.tang@intel.com
---
 arch/x86/kernel/fpu/xstate.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 0bab497..1afbc48 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -882,6 +882,13 @@ void __init fpu__init_system_xstate(unsigned int legacy_size)
 		goto out_disable;
 	}
 
+	/*
+	 * CPU capabilities initialization runs before FPU init. So
+	 * X86_FEATURE_OSXSAVE is not set. Now that XSAVE is completely
+	 * functional, set the feature bit so depending code works.
+	 */
+	setup_force_cpu_cap(X86_FEATURE_OSXSAVE);
+
 	print_xstate_offset_size();
 	pr_info("x86/fpu: Enabled xstate features 0x%llx, context size is %d bytes, using '%s' format.\n",
 		fpu_kernel_cfg.max_features,