The In-Field Scan [1] test does not start its operation when the CPU is unprepared. If the AMX state is uninitialized, the scan test will immediately terminate. Therefore, a proper initialization of the AMX state is necessary to run the test. Although fpu_idle_fpregs() initializes the state, its usage should be limited to specialized cases, primarily before entering the sleep state. The restore_fpregs_from_fpstate() function offers a suitable mechanism for initializing fpstate in general, which remains within the core code. Extend kernel_fpu_begin_mask() to include AMX state initialization, providing the in-field scan driver code access to the appropriate initialization method while maintaining compliance with established FPU API semantics. [1] https://docs.kernel.org/arch/x86/ifs.html Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx> --- The necessity for AMX initialization is clarified in the Intel Software Development Manual as of March 2024, particularly in Section 18.2 RECOMMENDATIONS FOR SYSTEM SOFTWARE of Vol. 1. Side note: restore_fpregs_from_fpstate() also sets the x87 state to a fixed value. However, this only applies to AMD CPUs with the FXSAVE_LEAK quirk. --- arch/x86/include/asm/fpu/api.h | 1 + arch/x86/kernel/fpu/core.c | 3 +++ 2 files changed, 4 insertions(+) diff --git a/arch/x86/include/asm/fpu/api.h b/arch/x86/include/asm/fpu/api.h index a2be3aefff9f..67887fc45c24 100644 --- a/arch/x86/include/asm/fpu/api.h +++ b/arch/x86/include/asm/fpu/api.h @@ -25,6 +25,7 @@ /* Kernel FPU states to initialize in kernel_fpu_begin_mask() */ #define KFPU_387 _BITUL(0) /* 387 state will be initialized */ #define KFPU_MXCSR _BITUL(1) /* MXCSR will be initialized */ +#define KFPU_AMX _BITUL(2) /* AMX will be initialized */ extern void kernel_fpu_begin_mask(unsigned int kfpu_mask); extern void kernel_fpu_end(void); diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c index 520deb411a70..0c0235b4a901 100644 --- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -440,6 +440,9 @@ void kernel_fpu_begin_mask(unsigned int kfpu_mask) if (unlikely(kfpu_mask & KFPU_387) && boot_cpu_has(X86_FEATURE_FPU)) asm volatile ("fninit"); + + if (unlikely(kfpu_mask & KFPU_AMX) && boot_cpu_has(X86_FEATURE_AMX_TILE)) + restore_fpregs_from_fpstate(&init_fpstate, XFEATURE_MASK_XTILE); } EXPORT_SYMBOL_GPL(kernel_fpu_begin_mask); -- 2.34.1
