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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@intel.com>
AuthorDate: Wed, 23 Aug 2023 14:57:47 +08:00
Committer: Thomas Gleixner <tglx@linutronix.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@intel.com>
Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.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,
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