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
