linux-kernel - Re: [PATCH v1 05/29] virtio-mem: generalize check for added memory

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Message-ID: <20201015082808.GE86495@L-31X9LVDL-1304.local>
Date:   Thu, 15 Oct 2020 16:28:08 +0800
From:   Wei Yang <richard.weiyang@...ux.alibaba.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        virtualization@...ts.linux-foundation.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Pankaj Gupta <pankaj.gupta.linux@...il.com>
Subject: Re: [PATCH v1 05/29] virtio-mem: generalize check for added memory

On Mon, Oct 12, 2020 at 02:52:59PM +0200, David Hildenbrand wrote:
>Let's check by traversing busy system RAM resources instead, to avoid
>relying on memory block states.
>
>Don't use walk_system_ram_range(), as that works on pages and we want to
>use the bare addresses we have easily at hand.
>
>Cc: "Michael S. Tsirkin" <mst@...hat.com>
>Cc: Jason Wang <jasowang@...hat.com>
>Cc: Pankaj Gupta <pankaj.gupta.linux@...il.com>
>Signed-off-by: David Hildenbrand <david@...hat.com>
>---
> drivers/virtio/virtio_mem.c | 19 +++++++++++++++----
> 1 file changed, 15 insertions(+), 4 deletions(-)
>
>diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
>index b3eebac7191f..6bbd1cfd10d3 100644
>--- a/drivers/virtio/virtio_mem.c
>+++ b/drivers/virtio/virtio_mem.c
>@@ -1749,6 +1749,20 @@ static void virtio_mem_delete_resource(struct virtio_mem *vm)
> 	vm->parent_resource = NULL;
> }
> 
>+static int virtio_mem_range_has_system_ram(struct resource *res, void *arg)
>+{
>+	return 1;
>+}
>+
>+static bool virtio_mem_has_memory_added(struct virtio_mem *vm)
>+{
>+	const unsigned long flags = IORESOURCE_SYSTEM_RAM | IORESOURCE_BUSY;
>+
>+	return walk_iomem_res_desc(IORES_DESC_NONE, flags, vm->addr,
>+				   vm->addr + vm->region_size, NULL,
>+				   virtio_mem_range_has_system_ram) == 1;
>+}
>+
> static int virtio_mem_probe(struct virtio_device *vdev)
> {
> 	struct virtio_mem *vm;
>@@ -1870,10 +1884,7 @@ static void virtio_mem_remove(struct virtio_device *vdev)
> 	 * the system. And there is no way to stop the driver/device from going
> 	 * away. Warn at least.
> 	 */
>-	if (vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE] ||
>-	    vm->nb_mb_state[VIRTIO_MEM_MB_STATE_OFFLINE_PARTIAL] ||
>-	    vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE] ||
>-	    vm->nb_mb_state[VIRTIO_MEM_MB_STATE_ONLINE_PARTIAL]) {
>+	if (virtio_mem_has_memory_added(vm)) {

I am not sure this would be more efficient.

> 		dev_warn(&vdev->dev, "device still has system memory added\n");
> 	} else {
> 		virtio_mem_delete_resource(vm);

BTW, I got one question during review.

Per my understanding, there are 4 states of a virtio memory block

  * OFFLINE[_PARTIAL]
  * ONLINE[_PARTIAL]

While, if my understanding is correct, those two offline states are transient.
If the required range is onlined, the state would be change to
ONLINE[_PARTIAL] respectively. If it is not, the state is reverted to UNUSED
or PLUGGED.

What I am lost is why you do virtio_mem_mb_remove() on OFFLINE_PARTIAL memory
block? Since we wait for the workqueue finish its job.

Also, during virtio_mem_remove(), we just handle OFFLINE_PARTIAL memory block.
How about memory block in other states? It is not necessary to remove
ONLINE[_PARTIAL] memroy blocks?

Thanks in advance, since I may missed some concepts.

>-- 
>2.26.2

-- 
Wei Yang
Help you, Help me