linux-kernel - Re: [PATCH for-next v6 4/7] RDMA/rxe: Add page invalidation support

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Message-ID: <ZPsuLeuGAgpBoTjU@ziepe.ca>
Date:   Fri, 8 Sep 2023 11:22:37 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Daisuke Matsuda <matsuda-daisuke@...itsu.com>
Cc:     linux-rdma@...r.kernel.org, leon@...nel.org, zyjzyj2000@...il.com,
        linux-kernel@...r.kernel.org, rpearsonhpe@...il.com,
        yangx.jy@...itsu.com, lizhijian@...itsu.com, y-goto@...itsu.com
Subject: Re: [PATCH for-next v6 4/7] RDMA/rxe: Add page invalidation support

On Fri, Sep 08, 2023 at 03:26:45PM +0900, Daisuke Matsuda wrote:
> On page invalidation, an MMU notifier callback is invoked to unmap DMA
> addresses and update the driver page table(umem_odp->dma_list). It also
> sets the corresponding entries in MR xarray to NULL to prevent any access.
> The callback is registered when an ODP-enabled MR is created.
> 
> Signed-off-by: Daisuke Matsuda <matsuda-daisuke@...itsu.com>
> ---
>  drivers/infiniband/sw/rxe/Makefile  |  2 +
>  drivers/infiniband/sw/rxe/rxe_odp.c | 64 +++++++++++++++++++++++++++++
>  2 files changed, 66 insertions(+)
>  create mode 100644 drivers/infiniband/sw/rxe/rxe_odp.c
> 
> diff --git a/drivers/infiniband/sw/rxe/Makefile b/drivers/infiniband/sw/rxe/Makefile
> index 5395a581f4bb..93134f1d1d0c 100644
> --- a/drivers/infiniband/sw/rxe/Makefile
> +++ b/drivers/infiniband/sw/rxe/Makefile
> @@ -23,3 +23,5 @@ rdma_rxe-y := \
>  	rxe_task.o \
>  	rxe_net.o \
>  	rxe_hw_counters.o
> +
> +rdma_rxe-$(CONFIG_INFINIBAND_ON_DEMAND_PAGING) += rxe_odp.o
> diff --git a/drivers/infiniband/sw/rxe/rxe_odp.c b/drivers/infiniband/sw/rxe/rxe_odp.c
> new file mode 100644
> index 000000000000..834fb1a84800
> --- /dev/null
> +++ b/drivers/infiniband/sw/rxe/rxe_odp.c
> @@ -0,0 +1,64 @@
> +// SPDX-License-Identifier: GPL-2.0 OR Linux-OpenIB
> +/*
> + * Copyright (c) 2022-2023 Fujitsu Ltd. All rights reserved.
> + */
> +
> +#include <linux/hmm.h>
> +
> +#include <rdma/ib_umem_odp.h>
> +
> +#include "rxe.h"
> +
> +static void rxe_mr_unset_xarray(struct rxe_mr *mr, unsigned long start,
> +				unsigned long end)
> +{
> +	unsigned long lower = rxe_mr_iova_to_index(mr, start);
> +	unsigned long upper = rxe_mr_iova_to_index(mr, end - 1);
> +	void *entry;
> +
> +	XA_STATE(xas, &mr->page_list, lower);
> +
> +	/* make elements in xarray NULL */
> +	xas_lock(&xas);
> +	while (true) {
> +		xas_store(&xas, NULL);
> +
> +		entry = xas_next(&xas);

I think this should just be

   xas_for_each(xas, entry, upper)
         xas_store(&xas, NULL)

> +		if (xas_retry(&xas, entry) || (xas.xa_index <= upper))
> +			continue;

xa_erase doesn't deal with retry entries, why do you think this does?

IIRC retry entries cannot be seen under the spinlock

Jason