Re: [PATCH v3 28/32] powerpc/64s: interrupt implement exit logic in C

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 25/02/2020 à 18:35, Nicholas Piggin a écrit :
> Implement the bulk of interrupt return logic in C. The asm return code
> must handle a few cases: restoring full GPRs, and emulating stack store.
> 
> The stack store emulation is significantly simplfied, rather than creating
> a new return frame and switching to that before performing the store, it
> uses the PACA to keep a scratch register around to perform thestore.
> 
> The asm return code is moved into 64e for now. The new logic has made
> allowance for 64e, but I don't have a full environment that works well
> to test it, and even booting in emulated qemu is not great for stress
> testing. 64e shouldn't be too far off working with this, given a bit
> more testing and auditing of the logic.
> 
> This is slightly faster on a POWER9 (page fault speed increases about
> 1.1%), probably due to reduced mtmsrd.
> 
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
> Signed-off-by: Michal Suchanek <msuchanek@suse.de>
> ---

...

> +notrace unsigned long interrupt_exit_user_prepare(struct pt_regs *regs, unsigned long msr)
> +{

...

> +
> +#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> +	local_paca->tm_scratch = regs->msr;
> +#endif

Could we define a helper for that in asm/tm.h, that voids when CONFIG_PPC_TRANSACTIONAL_MEM is not 
selected ?

> +
> +	kuap_check_amr();
> +
> +	account_cpu_user_exit();
> +
> +	return ret;
> +}
> +
> +void unrecoverable_exception(struct pt_regs *regs);
> +void preempt_schedule_irq(void);
> +
> +notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs, unsigned long msr)
> +{
> +

...

> +#ifdef CONFIG_PPC_TRANSACTIONAL_MEM
> +	local_paca->tm_scratch = regs->msr;
> +#endif
> +
> +	/*
> +	 * We don't need to restore AMR on the way back to userspace for KUAP.
> +	 * The value of AMR only matters while we're in the kernel.
> +	 */
> +	kuap_restore_amr(regs);
> +
> +	if (unlikely(*ti_flagsp & _TIF_EMULATE_STACK_STORE)) {
> +		clear_bits(_TIF_EMULATE_STACK_STORE, ti_flagsp);
> +		return 1;
> +	}
> +	return 0;
> +}
> +#endif

Christophe