lkml.org 
[lkml]   [2012]   [Jun]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Subject[PATCH v2 7/7] Flush page-table pages before freeing them
    From
    Date
    From: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>

    Certain architecture(viz. x86, arm, s390) have hardware page-table
    walkers(#PF). So during the RCU page-table teardown process make sure
    we do a tlb flush of page-table pages on all relevant CPUs to
    synchronize against hardware walkers, and then free the pages.

    Moreover, the (mm_users < 2) condition does not hold good for the above
    architectures, as the hardware engine is one of the user.

    Suggested-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Signed-off-by: Nikunj A. Dadhania <nikunj@linux.vnet.ibm.com>
    ---
    arch/Kconfig | 3 +++
    arch/x86/Kconfig | 12 ++++++++++++
    mm/memory.c | 24 ++++++++++++++++++++++--
    3 files changed, 37 insertions(+), 2 deletions(-)

    diff --git a/arch/Kconfig b/arch/Kconfig
    index 684eb5a..abc3739 100644
    --- a/arch/Kconfig
    +++ b/arch/Kconfig
    @@ -196,6 +196,9 @@ config HAVE_ARCH_MUTEX_CPU_RELAX
    config HAVE_RCU_TABLE_FREE
    bool

    +config ARCH_HW_WALKS_PAGE_TABLE
    + bool
    +
    config ARCH_HAVE_NMI_SAFE_CMPXCHG
    bool

    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index a9ec0da..b0a9f11 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -617,6 +617,18 @@ config PARAVIRT_SPINLOCKS

    If you are unsure how to answer this question, answer N.

    +config PARAVIRT_TLB_FLUSH
    + bool "Paravirtualization layer for TLB Flush"
    + depends on PARAVIRT && SMP && EXPERIMENTAL
    + select HAVE_RCU_TABLE_FREE
    + select ARCH_HW_WALKS_PAGE_TABLE
    + ---help---
    + Paravirtualized Flush TLB replace the native implementation
    + with something virtualization-friendly (for example, set a
    + flag for sleeping vcpu and do not wait for it).
    +
    + If you are unsure how to answer this question, answer N.
    +
    config PARAVIRT_CLOCK
    bool

    diff --git a/mm/memory.c b/mm/memory.c
    index c12685d..acfadb8 100644
    --- a/mm/memory.c
    +++ b/mm/memory.c
    @@ -335,11 +335,27 @@ static void tlb_remove_table_rcu(struct rcu_head *head)
    free_page((unsigned long)batch);
    }

    +#ifdef CONFIG_ARCH_HW_WALKS_PAGE_TABLE
    +/*
    + * Some architectures(x86, arm, s390) HW walks the page tables when
    + * the page-table tear down might be happening. So make sure that
    + * before freeing the page-table pages, flush their tlbs
    + */
    +static inline void tlb_table_flush_mmu(struct mmu_gather *tlb)
    +{
    + tlb_flush_mmu(tlb);
    +}
    +
    +#else
    +#define tlb_table_flush_mmu(tlb) do {} while (0)
    +#endif
    +
    void tlb_table_flush(struct mmu_gather *tlb)
    {
    struct mmu_table_batch **batch = &tlb->batch;

    if (*batch) {
    + tlb_table_flush_mmu(tlb);
    call_rcu_sched(&(*batch)->rcu, tlb_remove_table_rcu);
    *batch = NULL;
    }
    @@ -351,18 +367,22 @@ void tlb_remove_table(struct mmu_gather *tlb, void *table)

    tlb->need_flush = 1;

    +#ifndef CONFIG_ARCH_HW_WALKS_PAGE_TABLE
    /*
    - * When there's less then two users of this mm there cannot be a
    - * concurrent page-table walk.
    + * When there's less then two users of this mm there cannot be
    + * a concurrent page-table walk for architectures that do not
    + * have hardware page-table walkers.
    */
    if (atomic_read(&tlb->mm->mm_users) < 2) {
    __tlb_remove_table(table);
    return;
    }
    +#endif

    if (*batch == NULL) {
    *batch = (struct mmu_table_batch *)__get_free_page(GFP_NOWAIT | __GFP_NOWARN);
    if (*batch == NULL) {
    + tlb_table_flush_mmu(tlb);
    tlb_remove_table_one(table);
    return;
    }


    \
     
     \ /
      Last update: 2012-06-04 07:42    [W:0.032 / U:36.324 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site