Messages in this thread |  | | Date | Sat, 25 Nov 2017 18:25:33 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH v2 2/2] x86: disable IRQs before changing CR4 |
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On Sat, 25 Nov 2017, Nadav Amit wrote: > Thomas Gleixner <tglx@linutronix.de> wrote: > > > On Fri, 24 Nov 2017, Nadav Amit wrote: > >> /* Set in this cpu's CR4. */ > >> -static inline void cr4_set_bits(unsigned long mask) > >> +static inline void cr4_set_bits_irqs_off(unsigned long mask) > > > > This change is kinda weird. I'd expect that there is a corresponding > > function cr4_set_bits() which takes care of disabling interrupts. But there > > is not. All it does is creating a lot of pointless churn. > > > >> static __always_inline void setup_smep(struct cpuinfo_x86 *c) > >> static __init int setup_disable_smap(char *arg) > >> static __always_inline void setup_pku(struct cpuinfo_x86 *c) > > > > Why are you not doing this at the call site around all calls which fiddle > > with cr4, i.e. in identify_cpu() ? > > > > identify_cpu() is called from two places: > > > > identify_boot_cpu() and identify_secondary_cpu() > > > > identify_secondary_cpu is called with interrupts disabled anyway and there > > is no reason why we can't enforce interrupts being disabled around > > identify_cpu() completely. > > > > But if we actually do the right thing, i.e. having cr4_set_bit() and > > cr4_set_bit_irqsoff() all of this churn goes away magically. > > > > Then the only place which needs to be changed is the context switch because > > here interrupts are already disabled and we really care about performance. > > > >> @@ -293,7 +303,7 @@ void __switch_to_xtra(struct task_struct *prev_p, struct task_struct *next_p, > >> } > >> > >> if ((tifp ^ tifn) & _TIF_NOTSC) > >> - cr4_toggle_bits(X86_CR4_TSD); > >> + cr4_toggle_bits_irqs_off(X86_CR4_TSD); > > You make a good point. I will add cr4_set_bit(). I will leave identify_cpu() > as is, since it is rather hard to maintain code that enables/disables irqs > at one point and rely on these operations at a completely different place. > As you said, it is less of an issue once cr4_set_bit() and friends are > introduced.
I fixed that up already as I wanted to have it done, see the tip-bot mail in your inbox.
Thanks,
tglx
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