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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 14, 2025 at 03:53:00PM +0300, Mika Penttilä wrote: > > On 8/14/25 15:40, Jason Gunthorpe wrote: > > On Thu, Aug 14, 2025 at 10:19:26AM +0300, Mika Penttilä wrote: > >> When doing migration in combination with device fault handling, > >> detect the case in the interval notifier. > >> > >> Without that, we would livelock with our own invalidations > >> while migrating and splitting pages during fault handling. > >> > >> Note, pgmap_owner, used in some other code paths as owner for filtering, > >> is not readily available for split path, so use current for this use case. > >> Also, current and pgmap_owner, both being pointers to memory, can not be > >> mis-interpreted to each other. > >> > >> Cc: David Hildenbrand > >> Cc: Jason Gunthorpe > >> Cc: Leon Romanovsky > >> Cc: Alistair Popple > >> Cc: Balbir Singh > >> > >> Signed-off-by: Mika Penttilä > >> --- > >> lib/test_hmm.c | 5 +++++ > >> mm/huge_memory.c | 6 +++--- > >> mm/rmap.c | 4 ++-- > >> 3 files changed, 10 insertions(+), 5 deletions(-) > >> > >> diff --git a/lib/test_hmm.c b/lib/test_hmm.c > >> index 761725bc713c..cd5c139213be 100644 > >> --- a/lib/test_hmm.c > >> +++ b/lib/test_hmm.c > >> @@ -269,6 +269,11 @@ static bool dmirror_interval_invalidate(struct mmu_interval_notifier *mni, > >> range->owner == dmirror->mdevice) > >> return true; > >> > >> + if (range->event == MMU_NOTIFY_CLEAR && > >> + range->owner == current) { > >> + return true; > >> + } > > I don't understand this, there is nothing in hmm that says only > > current can call hmm_range_fault, and indeed most applications won't > > even gurantee that. > > No it's the opposite, if we are ourselves the invalidator, don't care. I think you've missed the point, you cannot use range->owner in any way to tell "we are ourselves the invalidator". It is simply not the meaning of range->owner. > > So if this plan relies on something like the above in drivers I don't > > see how it can work. > > > > If this is just some hack for tests, try instead to find a solution > > that more accurately matches what a real driver should do. > > > > But this also seems overall troublesome to your goal, if you do a > > migrate inside hmm_range_fault() it will generate an invalidation call > > back and that will increment the seqlock and we will loop > > hmm_range_fault() again which rewalks. > > That's the problem this solves. > The semantics is "if we are the invalidator don't wait for invalidate end", > aka don't mmu_interval_set_seq() that would make hang in the next mmu_interval_read_begin(), > waiting the invalidate to end I doubt we can skip mmu_interval_set_seq(), doing so can corrupt concurrent hmm_range_fault in some other thread. Nor, as I said, can we actually skip the invalidation toward HW anyhow. At the very least this commit message fails to explain the new locking proposal, or justify why it can work. Jason