| Message ID | 20191217071713.93399-2-aneesh.kumar@linux.ibm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [RFC,1/2] mm/mmu_gather: Invalidate TLB correctly on batch allocation failure and flush | expand |
On Tue, Dec 17, 2019 at 12:47:13PM +0530, Aneesh Kumar K.V wrote: > On tlb_finish_mmu() kernel does a tlb flush before mmu gather table invalidate. > The mmu gather table invalidate depending on kernel config also does another > TLBI. Avoid the later on tlb_finish_mmu(). That is already avoided, if you look at tlb_flush_mmu_tlbonly() it does __tlb_range_reset(), which results in ->end = 0, which then triggers the early exit on the next invocation: if (!tlb->end) return;
On 12/17/19 2:28 PM, Peter Zijlstra wrote: > On Tue, Dec 17, 2019 at 12:47:13PM +0530, Aneesh Kumar K.V wrote: >> On tlb_finish_mmu() kernel does a tlb flush before mmu gather table invalidate. >> The mmu gather table invalidate depending on kernel config also does another >> TLBI. Avoid the later on tlb_finish_mmu(). > > That is already avoided, if you look at tlb_flush_mmu_tlbonly() it does > __tlb_range_reset(), which results in ->end = 0, which then triggers the > early exit on the next invocation: > > if (!tlb->end) > return; > Is that true for tlb->fulmm flush? -aneesh
On Tue, Dec 17, 2019 at 03:45:36PM +0530, Aneesh Kumar K.V wrote: > On 12/17/19 2:28 PM, Peter Zijlstra wrote: > > On Tue, Dec 17, 2019 at 12:47:13PM +0530, Aneesh Kumar K.V wrote: > > > On tlb_finish_mmu() kernel does a tlb flush before mmu gather table invalidate. > > > The mmu gather table invalidate depending on kernel config also does another > > > TLBI. Avoid the later on tlb_finish_mmu(). > > > > That is already avoided, if you look at tlb_flush_mmu_tlbonly() it does > > __tlb_range_reset(), which results in ->end = 0, which then triggers the > > early exit on the next invocation: > > > > if (!tlb->end) > > return; > > > > Is that true for tlb->fulmm flush? Hmm, no, but I'm thinking you patch is broken, even for that case. We must issue the TLBI before call_rcu(). Perhaps if we replace !tlb->end with something like: !tlb->freed_tables && !tlb->cleared_p* (which GCC should be able to do with a single load and mask) I've not really thought too hard about it yet, I need to run some errands, but I'll look at it more closely when I get back.
diff --git a/mm/mmu_gather.c b/mm/mmu_gather.c index 7c1b8f67af7b..7e2bd43b9084 100644 --- a/mm/mmu_gather.c +++ b/mm/mmu_gather.c @@ -143,17 +143,23 @@ static void tlb_remove_table_rcu(struct rcu_head *head) free_page((unsigned long)batch); } -static void tlb_table_flush(struct mmu_gather *tlb) +static void __tlb_table_flush(struct mmu_gather *tlb, bool table_inval) { struct mmu_table_batch **batch = &tlb->batch; if (*batch) { - tlb_table_invalidate(tlb); + if (table_inval) + tlb_table_invalidate(tlb); call_rcu(&(*batch)->rcu, tlb_remove_table_rcu); *batch = NULL; } } +static void tlb_table_flush(struct mmu_gather *tlb) +{ + __tlb_table_flush(tlb, true); +} + void tlb_remove_table(struct mmu_gather *tlb, void *table) { struct mmu_table_batch **batch = &tlb->batch; @@ -178,7 +184,7 @@ void tlb_remove_table(struct mmu_gather *tlb, void *table) static void tlb_flush_mmu_free(struct mmu_gather *tlb) { #ifdef CONFIG_HAVE_RCU_TABLE_FREE - tlb_table_flush(tlb); + __tlb_table_flush(tlb, false); #endif #ifndef CONFIG_HAVE_MMU_GATHER_NO_GATHER tlb_batch_pages_flush(tlb);
On tlb_finish_mmu() kernel does a tlb flush before mmu gather table invalidate. The mmu gather table invalidate depending on kernel config also does another TLBI. Avoid the later on tlb_finish_mmu(). Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> --- mm/mmu_gather.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-)