On Tue, Apr 30, 2024 at 02:25:07PM -0700, Bae, Chang Seok wrote: > 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. Instead of using new terminology like "unprepared", maybe use the term "non-initialized state" as in the SDM for clarity? Maintaining AMX state in a non-initialized state will prevent In-field Scan test [1] to abort without making progress. > > 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. Maybe simplify the above paragraph with Extend kernel_fpu_begin_mask() to allow In-field scan driver to initialize AMX state before running tests. > > [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 > -- Cheers, Ashok
