linux-kernel - [PATCH] x86/fpu: set X86_FEATURE_OSXSAVE feature after enabling OSXSAVE in CR4

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Message-Id: <20230823065747.92257-1-feng.tang@intel.com>
Date:   Wed, 23 Aug 2023 14:57:47 +0800
From:   Feng Tang <feng.tang@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...el.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        kernel test robot <oliver.sang@...el.com>,
        linux-kernel@...r.kernel.org
Cc:     Feng Tang <feng.tang@...el.com>
Subject: [PATCH] x86/fpu: set X86_FEATURE_OSXSAVE feature after enabling OSXSAVE in CR4

0Day found a 34.6% regression in stress-ng's 'af-alg' test case [1], 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);

And it makes 'X86_FEATURE_OSXSAVE' feature bit missed in cpu capability
setup. Many security module like 'camellia_aesni_avx_x86_64' depends on
this feature, and will fail to be loaded after the commit, causing the
regression.

So set X86_FEATURE_OSXSAVE feature right after OSXSAVE enabling to fix it.

[1]. https://lore.kernel.org/lkml/202307192135.203ac24e-oliver.sang@intel.com/

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>
---
 arch/x86/kernel/fpu/xstate.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 0bab497c9436..8ebea0d522d2 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -173,6 +173,9 @@ void fpu__init_cpu_xstate(void)
 
 	cr4_set_bits(X86_CR4_OSXSAVE);
 
+	if (!boot_cpu_has(X86_FEATURE_OSXSAVE))
+		setup_force_cpu_cap(X86_FEATURE_OSXSAVE);
+
 	/*
 	 * Must happen after CR4 setup and before xsetbv() to allow KVM
 	 * lazy passthrough.  Write independent of the dynamic state static
-- 
2.27.0