Messages in this thread | | | Date | Tue, 22 Jun 2021 17:38:24 +0200 | From | Borislav Petkov <> | Subject | Re: [patch V3 47/66] x86/fpu: Clean up the fpu__clear() variants |
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Only nitpicks:
On Fri, Jun 18, 2021 at 04:19:10PM +0200, Thomas Gleixner wrote: > From: Andy Lutomirski <luto@kernel.org> > > fpu__clear() currently resets both register state and kernel XSAVE buffer > state. It has two modes: one for all state (supervisor and user) and > another for user state only. fpu__clear_all() uses the "all state" > (user_only=0) mode, while a number of signal paths use the user_only=1 > mode. > > Make fpu__clear() work only for user state (user_only=1) and remove the > "all state" (user_only=0) code. Rename it to match so it can be used by > the signal paths. > > Replace the "all state" (user_only=0) fpu__clear() functionality. Use the > TIF_NEED_FPU_LOAD functionality instead of making any actual hardware > registers changes in this path. > > Instead of invoking fpu__initialize() just memcpy() init_fpstate into the > tasks FPU state because that has already the correct format and in case of
task's
> PKRU also contains the default PKRU value. Move the actual PKRU write out > into flush_thread() where it belongs and where it will end up anyway when > PKRU and XSTATE have been distangled.
untangled
> > For bisectability a workaround is required which stores the PKRU value in > the xstate memory until PKRU is distangled from XSTATE for context
untangled
> switching and return to user. > > [ Dave Hansen: Polished changelog ] > [ tglx: Fixed the PKRU fallout ] > > Signed-off-by: Andy Lutomirski <luto@kernel.org> > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > --- > arch/x86/kernel/fpu/core.c | 111 ++++++++++++++++++++++++++++++--------------- > arch/x86/kernel/process.c | 10 ++++ > 2 files changed, 85 insertions(+), 36 deletions(-)
...
> +/* Temporary workaround. Will be removed once PKRU and XSTATE are distangled. */
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(); > +} > + > /* > - * Clear the FPU state back to init state. > - * > - * Called by sys_execve(), by the signal handler code and by various > - * error paths. > + * Reset current->fpu memory state to the init values. > */ > -static void fpu__clear(struct fpu *fpu, bool user_only) > +static void fpu_reset_fpstate(void) > +{ > + struct fpu *fpu= ¤t->thread.fpu;
ERROR: spaces required around that '=' (ctx:VxW) #167: FILE: arch/x86/kernel/fpu/core.c:335: + struct fpu *fpu= ¤t->thread.fpu; ^
> + > + fpregs_lock(); > + fpu__drop(fpu); > + /* > + * This does not change the actual hardware registers. It just > + * resets the memory image and sets TIF_NEED_FPU_LOAD so a > + * subsequent return to usermode will reload the registers from the > + * tasks memory image.
task's
> + * > + * Do not use fpstate_init() here. Just copy init_fpstate which has > + * the correct content already except for PKRU. > + */
Dunno, this comment can be over the function name - it is small enough anyway.
> + 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(); > +} > + > +/* > + * Reset current's user FPU states to the init states. current's > + * supervisor states, if any, are not modified by this function. The > + * caller guarantees that the XSTATE header in memory is intact. > + */ > +void fpu__clear_user_states(struct fpu *fpu) > { > WARN_ON_FPU(fpu != ¤t->thread.fpu); > > + fpregs_lock(); > if (!static_cpu_has(X86_FEATURE_FPU)) {
cpu_feature_enabled()
> - fpu__drop(fpu); > - fpu__initialize(fpu); > + fpu_reset_fpstate(); > + fpregs_unlock(); > return; > } > > - fpregs_lock(); > - > - if (user_only) { > - if (!fpregs_state_valid(fpu, smp_processor_id()) && > - xfeatures_mask_supervisor()) > - os_xrstor(&fpu->state.xsave, xfeatures_mask_supervisor()); > - load_fpregs_from_init_fpstate(xfeatures_mask_user()); > - } else { > - load_fpregs_from_init_fpstate(xfeatures_mask_all); > + /* > + * Ensure that current's supervisor states are loaded into their > + * corresponding registers. > + */ > + if (xfeatures_mask_supervisor() && > + !fpregs_state_valid(fpu, smp_processor_id())) { > + os_xrstor(&fpu->state.xsave, xfeatures_mask_supervisor()); > } > > + /* Reset user states in registers. */ > + load_fpregs_from_init_fpstate(xfeatures_mask_user()); > + > + /* > + * Now all FPU registers have their desired values. Inform the FPU > + * state machine that current's FPU registers are in the hardware > + * registers. The memory image does not need to be updated because > + * any operation relying on it has to save the registers first when > + * currents FPU is marked active.
current's
> + */ > fpregs_mark_activate(); > fpregs_unlock(); > } >
-- Regards/Gruss, Boris.
SUSE Software Solutions Germany GmbH, GF: Felix Imendörffer, HRB 36809, AG Nürnberg
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