Re: [dpdk-dev] [PATCH 3/3] net/virtio-user: fix memory hotplug support in vhost-kernel

["Burakov, Anatoly" <anatoly.burakov@intel.com>]

On 10-Sep-18 5:04 AM, Tiwei Bie wrote:
> On Fri, Sep 07, 2018 at 01:24:05PM +0100, Burakov, Anatoly wrote:
>> On 07-Sep-18 12:37 PM, Tiwei Bie wrote:
>>> On Fri, Sep 07, 2018 at 10:44:22AM +0100, Burakov, Anatoly wrote:
>>>> On 05-Sep-18 5:28 AM, Tiwei Bie wrote:
>>>>> It's possible to have much more hugepage backed memory regions
>>>>> than what vhost-kernel supports due to the memory hotplug, which
>>>>> may cause problems. A better solution is to have the virtio-user
>>>>> pass all the memory ranges reserved by DPDK to vhost-kernel.
>>>>>
>>>>> Fixes: 12ecb2f63b12 ("net/virtio-user: support memory hotplug")
>>>>> Cc: stable@dpdk.org
>>>>>
>>>>> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
>>>>> ---
>>>>>     drivers/net/virtio/virtio_user/vhost_kernel.c | 38 +++++++++----------
>>>>>     1 file changed, 18 insertions(+), 20 deletions(-)
>>>>>
>>>>> diff --git a/drivers/net/virtio/virtio_user/vhost_kernel.c b/drivers/net/virtio/virtio_user/vhost_kernel.c
>>>>> index 897fee0af..9338166d9 100644
>>>>> --- a/drivers/net/virtio/virtio_user/vhost_kernel.c
>>>>> +++ b/drivers/net/virtio/virtio_user/vhost_kernel.c
>>>>> @@ -70,41 +70,41 @@ static uint64_t vhost_req_user_to_kernel[] = {
>>>>>     	[VHOST_USER_SET_MEM_TABLE] = VHOST_SET_MEM_TABLE,
>>>>>     };
>>>>> -struct walk_arg {
>>>>> -	struct vhost_memory_kernel *vm;
>>>>> -	uint32_t region_nr;
>>>>> -};
>>>>>     static int
>>>>> -add_memory_region(const struct rte_memseg_list *msl __rte_unused,
>>>>> -		const struct rte_memseg *ms, size_t len, void *arg)
>>>>> +add_memseg_list(const struct rte_memseg_list *msl, void *arg)
>>>>>     {
>>>>> -	struct walk_arg *wa = arg;
>>>>> +	struct vhost_memory_kernel *vm = arg;
>>>>>     	struct vhost_memory_region *mr;
>>>>>     	void *start_addr;
>>>>> +	uint64_t len;
>>>>> -	if (wa->region_nr >= max_regions)
>>>>> +	if (vm->nregions >= max_regions)
>>>>>     		return -1;
>>>>> -	mr = &wa->vm->regions[wa->region_nr++];
>>>>> -	start_addr = ms->addr;
>>>>> +	start_addr = msl->base_va;
>>>>> +	len = msl->page_sz * msl->memseg_arr.len;
>>>>> +
>>>>> +	mr = &vm->regions[vm->nregions++];
>>>>>     	mr->guest_phys_addr = (uint64_t)(uintptr_t)start_addr;
>>>>>     	mr->userspace_addr = (uint64_t)(uintptr_t)start_addr;
>>>>>     	mr->memory_size = len;
>>>>> -	mr->mmap_offset = 0;
>>>>> +	mr->mmap_offset = 0; /* flags_padding */
>>>>> +
>>>>> +	PMD_DRV_LOG(DEBUG, "index=%u addr=%p len=%" PRIu64,
>>>>> +			vm->nregions - 1, start_addr, len);
>>>>>     	return 0;
>>>>>     }
>>>>> -/* By default, vhost kernel module allows 64 regions, but DPDK allows
>>>>> - * 256 segments. As a relief, below function merges those virtually
>>>>> - * adjacent memsegs into one region.
>>>>> +/* By default, vhost kernel module allows 64 regions, but DPDK may
>>>>> + * have much more memory regions. Below function will treat each
>>>>> + * contiguous memory space reserved by DPDK as one region.
>>>>>      */
>>>>>     static struct vhost_memory_kernel *
>>>>>     prepare_vhost_memory_kernel(void)
>>>>>     {
>>>>>     	struct vhost_memory_kernel *vm;
>>>>> -	struct walk_arg wa;
>>>>>     	vm = malloc(sizeof(struct vhost_memory_kernel) +
>>>>>     			max_regions *
>>>>> @@ -112,20 +112,18 @@ prepare_vhost_memory_kernel(void)
>>>>>     	if (!vm)
>>>>>     		return NULL;
>>>>> -	wa.region_nr = 0;
>>>>> -	wa.vm = vm;
>>>>> +	vm->nregions = 0;
>>>>> +	vm->padding = 0;
>>>>>     	/*
>>>>>     	 * The memory lock has already been taken by memory subsystem
>>>>>     	 * or virtio_user_start_device().
>>>>>     	 */
>>>>> -	if (rte_memseg_contig_walk_thread_unsafe(add_memory_region, &wa) < 0) {
>>>>> +	if (rte_memseg_list_walk_thread_unsafe(add_memseg_list, vm) < 0) {
>>>>>     		free(vm);
>>>>>     		return NULL;
>>>>>     	}
>>>>> -	vm->nregions = wa.region_nr;
>>>>> -	vm->padding = 0;
>>>>>     	return vm;
>>>>>     }
>>>>>
>>>>
>>>> Doesn't that assume single file segments mode?
>>>
>>> This is to find out the VA ranges reserved by memory subsystem.
>>> Why does it need to assume single file segments mode?
>>
>> If you are not in single-file segments mode, each individual page in a
>> VA-contiguous area will be behind a different fd - so it will be part of a
>> different region, would it not?
> 
> Above code is for vhost-kernel. Kernel doesn't need the
> fds to get the access to virtio-user process's memory.
> Kernel just needs to know the mappings between GPA (guest
> physical address) and VA (virtio-user's virtual address).
> 

Ah OK. Thanks for clarification!

-- 
Thanks,
Anatoly