Re: [PATCH v3 hmm 05/11] hmm: use mmu_notifier_get/put for 'struct hmm'

From: Ralph Campbell
Date: Wed Aug 14 2019 - 17:51:12 EST

On 8/6/19 4:15 PM, Jason Gunthorpe wrote:
From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>

This is a significant simplification, it eliminates all the remaining
'hmm' stuff in mm_struct, eliminates krefing along the critical notifier
paths, and takes away all the ugly locking and abuse of page_table_lock.

mmu_notifier_get() provides the single struct hmm per struct mm which
eliminates mm->hmm.

It also directly guarantees that no mmu_notifier op callback is callable
while concurrent free is possible, this eliminates all the krefs inside
the mmu_notifier callbacks.

The remaining krefs in the range code were overly cautious, drivers are
already not permitted to free the mirror while a range exists.

Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>

Looks good.
Reviewed-by: Ralph Campbell <rcampbell@xxxxxxxxxx>