Re: [PATCH rdma-next] RDMA/rxe: Break endless pagefault loop for RO pages

[Leon Romanovsky <leon@kernel.org>]

On Thu, May 22, 2025 at 10:29:02PM +0900, Daisuke Matsuda wrote:
> 
> On 2025/05/22 20:36, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@nvidia.com>
> > 
> > RO pages has "perm" equal to 0, that caused to the situation
> > where such pages were marked as needed to have fault and caused
> > to infinite loop.
> > 
> > Fixes: eedd5b1276e7 ("RDMA/umem: Store ODP access mask information in PFN")
> > Reported-by: Daisuke Matsuda <dskmtsd@gmail.com>
> > Closes: https://lore.kernel.org/all/3e8f343f-7d66-4f7a-9f08-3910623e322f@gmail.com
> > Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
> 
> Tested-by: Daisuke Matsuda <dskmtsd@gmail.com>
> 
> Thank you!
> This change fixes one of the two issues I reported.
> The kernel module does not get stuck in rxe_ib_invalidate_range() anymore.
> 
> 
> The remaining one is the stuck issue in uverbs_destroy_ufile_hw().
> cf. https://lore.kernel.org/all/3e8f343f-7d66-4f7a-9f08-3910623e322f@gmail.com/

Thanks, I updated the link to point to https://lore.kernel.org/all/3016329a-4edd-4550-862f-b298a1b79a39@gmail.com/

> 
> The issue occurs with test_odp_async_prefetch_rc_traffic, which is not yet
> enabled in rxe. It might indicate that the root cause lies in ib_uverbs layer.

Unlikely, up till now, it indicated that driver didn't release some
uverb object.

> I will take a closer look anyway.
> 
> Thanks,
> Daisuke
> 
> 
> > ---
> >   drivers/infiniband/sw/rxe/rxe_odp.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/infiniband/sw/rxe/rxe_odp.c b/drivers/infiniband/sw/rxe/rxe_odp.c
> > index a1416626f61a5..0f67167ddddd1 100644
> > --- a/drivers/infiniband/sw/rxe/rxe_odp.c
> > +++ b/drivers/infiniband/sw/rxe/rxe_odp.c
> > @@ -137,7 +137,7 @@ static inline bool rxe_check_pagefault(struct ib_umem_odp *umem_odp,
> >   	while (addr < iova + length) {
> >   		idx = (addr - ib_umem_start(umem_odp)) >> umem_odp->page_shift;
> > -		if (!(umem_odp->map.pfn_list[idx] & perm)) {
> > +		if (!(umem_odp->map.pfn_list[idx] & HMM_PFN_VALID)) {
> >   			need_fault = true;
> >   			break;
> >   		}
>