| Date | Wed, 23 Jun 2021 14:02:22 +0200 | From | Thomas Gleixner <> | Subject | [patch V4 55/65] x86/fpu: Dont store PKRU in xstate in fpu_reset_fpstate() |
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PKRU for a task is stored in task->thread.pkru when the task is scheduled out. For 'current' the authoritative source of PKRU is the hardware.
fpu_reset_fpstate() has two callers:
1) fpu__clear_user_states() for !FPU systems. For those PKRU is irrelevant
2) fpu_flush_thread() which is invoked from flush_thread(). flush_thread() resets the hardware to the kernel restrictive default value.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Borislav Petkov <bp@suse.de> --- arch/x86/kernel/fpu/core.c | 22 ++++------------------ 1 file changed, 4 insertions(+), 18 deletions(-)
--- a/arch/x86/kernel/fpu/core.c +++ b/arch/x86/kernel/fpu/core.c @@ -337,23 +337,6 @@ static inline unsigned int init_fpstate_ return sizeof(init_fpstate.xsave); } -/* Temporary workaround. Will be removed once PKRU and XSTATE are untangled. */ -static inline void pkru_set_default_in_xstate(struct xregs_state *xsave) -{ - struct pkru_state *pk; - - if (!cpu_feature_enabled(X86_FEATURE_OSPKE)) - return; - /* - * Force XFEATURE_PKRU to be set in the header otherwise - * get_xsave_addr() does not work and it also needs to be set to - * make XRSTOR(S) load it. - */ - xsave->header.xfeatures |= XFEATURE_MASK_PKRU; - pk = get_xsave_addr(xsave, XFEATURE_PKRU); - pk->pkru = pkru_get_init_value(); -} - /* * Reset current->fpu memory state to the init values. */ @@ -371,9 +354,12 @@ static void fpu_reset_fpstate(void) * * Do not use fpstate_init() here. Just copy init_fpstate which has * the correct content already except for PKRU. + * + * PKRU handling does not rely on the xstate when restoring for + * user space as PKRU is eagerly written in switch_to() and + * flush_thread(). */ memcpy(&fpu->state, &init_fpstate, init_fpstate_copy_size()); - pkru_set_default_in_xstate(&fpu->state.xsave); set_thread_flag(TIF_NEED_FPU_LOAD); fpregs_unlock(); }
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