Hey Andy > > Context switches and TLB flushes can change individual bits of CR4. > CR4 reads take several cycles, so store a shadow copy of CR4 in a > per-cpu variable. > > To avoid wasting a cache line, I added the CR4 shadow to > cpu_tlbstate, which is already touched during context switches. > > Signed-off-by: Andy Lutomirski <[email protected]> > --- > arch/x86/include/asm/tlbflush.h | 52 > ++++++++++++++++++++++++++++++----------- > arch/x86/kernel/cpu/common.c | 7 ++++++ > arch/x86/kernel/head32.c | 1 + > arch/x86/kernel/head64.c | 2 ++ > arch/x86/kvm/vmx.c | 4 ++-- > arch/x86/mm/init.c | 8 +++++++ > arch/x86/mm/tlb.c | 3 --- > 7 files changed, 59 insertions(+), 18 deletions(-) > > diff --git a/arch/x86/include/asm/tlbflush.h > b/arch/x86/include/asm/tlbflush.h > index 95b672f8b493..a04cad4bcbc3 100644 > --- a/arch/x86/include/asm/tlbflush.h > +++ b/arch/x86/include/asm/tlbflush.h > @@ -15,14 +15,37 @@ > #define __flush_tlb_single(addr) __native_flush_tlb_single(addr) > #endif > > +struct tlb_state { > +#ifdef CONFIG_SMP > + struct mm_struct *active_mm; > + int state; > +#endif > + > + /* > + * Access to this CR4 shadow and to H/W CR4 is protected by > + * disabling interrupts when modifying either one. > + */ > + unsigned long cr4; > +}; > +DECLARE_PER_CPU_SHARED_ALIGNED(struct tlb_state, cpu_tlbstate); > + > +/* Initialize cr4 shadow for this CPU. */ > +static inline void cr4_init_shadow(void) > +{ > + this_cpu_write(cpu_tlbstate.cr4, read_cr4()); > +} > + > /* Set in this cpu's CR4. */ > static inline void cr4_set(unsigned long mask) > { > unsigned long cr4; > > - cr4 = read_cr4(); > - cr4 |= mask; > - write_cr4(cr4); > + cr4 = this_cpu_read(cpu_tlbstate.cr4); > + if (!(cr4 & mask)) {
What if cr4 contains bit_A and mask contains bits A and B? Hillf > + cr4 |= mask; > + this_cpu_write(cpu_tlbstate.cr4, cr4); > + write_cr4(cr4); > + } > } > [...] -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
