On Fri, Jun 2, 2023 at 6:33 PM Matt Turner <mattst88@xxxxxxxxx> wrote:
>
> On Wed, May 24, 2023 at 1:18 PM Nicholas Piggin <npiggin@xxxxxxxxx> wrote:
> >
> > mm_cpumask is a map of the CPUs which must be IPIed to flush TLBs,
> > and/or IPIed to shootdown lazy TLB mms at exit time.
> >
> > When flushing TLBs on the CPU, trim it from mm_cpumask if the mm is not
> > currently active on the CPU. TLBs will have been flush, and the mm is
> > not active, so there is no more reason to get IPIs.
> >
> > Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
> > ---
> > arch/alpha/include/asm/tlbflush.h | 3 +++
> > arch/alpha/kernel/smp.c | 29 +++++++++++++++++++++++++++--
> > 2 files changed, 30 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/alpha/include/asm/tlbflush.h b/arch/alpha/include/asm/tlbflush.h
> > index 94dc37cf873a..7c4e719ac9e7 100644
> > --- a/arch/alpha/include/asm/tlbflush.h
> > +++ b/arch/alpha/include/asm/tlbflush.h
> > @@ -12,6 +12,7 @@
> > #endif
> >
> > extern void __load_new_mm_context(struct mm_struct *);
> > +extern void try_clear_mm_cpumask(struct mm_struct *);
> >
> >
> > /* Use a few helper functions to hide the ugly broken ASN
> > @@ -106,6 +107,7 @@ static inline void flush_tlb_all(void)
> > static inline void
> > flush_tlb_mm(struct mm_struct *mm)
> > {
> > + try_clear_mm_cpumask(mm);
> > if (mm == current->active_mm)
> > flush_tlb_current(mm);
> > else
> > @@ -118,6 +120,7 @@ flush_tlb_page(struct vm_area_struct *vma, unsigned long addr)
> > {
> > struct mm_struct *mm = vma->vm_mm;
> >
> > + try_clear_mm_cpumask(mm);
> > if (mm == current->active_mm)
> > flush_tlb_current_page(mm, vma, addr);
> > else
> > diff --git a/arch/alpha/kernel/smp.c b/arch/alpha/kernel/smp.c
> > index e436c056267d..d668b9d319af 100644
> > --- a/arch/alpha/kernel/smp.c
> > +++ b/arch/alpha/kernel/smp.c
> > @@ -610,6 +610,28 @@ smp_imb(void)
> > }
> > EXPORT_SYMBOL(smp_imb);
> >
> > +#define asn_locked() (cpu_data[smp_processor_id()].asn_lock)
> > +
> > +/*
> > + * If the mm_cpumask bit is cleared, the caller *must* flush the TLB for the
> > + * mm on this CPU. It is only cleared when the mm is not active, in which
> > + * case the flushing always performs flush_tlb_other that flushes everything.
> > + * If that changes in callers, they will have to arrange to always do a full
> > + * flush if mm_cpumask is cleared by this function.
> > + */
> > +void
> > +try_clear_mm_cpumask(struct mm_struct *mm)
> > +{
> > + int cpu;
> > +
> > + if (current->active_mm == mm || asn_locked())
> > + return;
> > +
> > + cpu = smp_processor_id();
> > + if (cpumask_test_cpu(cpu, mm_cpumask(mm)))
> > + cpumask_clear_cpu(cpu, mm_cpumask(mm));
> > +}
>
> Since this is implemented in smp.c, the function is not available in
> !CONFIG_SMP:
>
> ld: kernel/fork.o: in function `dup_mmap':
> (.text+0x1734): undefined reference to `try_clear_mm_cpumask'
> ld: (.text+0x1738): undefined reference to `try_clear_mm_cpumask'
> ld: mm/memory.o: in function `unmap_page_range':
> (.text+0x1934): undefined reference to `try_clear_mm_cpumask'
> ld: (.text+0x193c): undefined reference to `try_clear_mm_cpumask'
> ld: (.text+0x1a28): undefined reference to `try_clear_mm_cpumask'
> ld: mm/memory.o:(.text+0x1a30): more undefined references to
> `try_clear_mm_cpumask' follow
> make[1]: *** [scripts/Makefile.vmlinux:35: vmlinux] Error 1
> make: *** [Makefile:1249: vmlinux] Error 2
Anything I can do to help?
