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

[Tiwei Bie <tiwei.bie@intel.com>]

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).


> 
> > 
> > 
> > > 
> > > -- 
> > > Thanks,
> > > Anatoly
> > 
> 
> 
> -- 
> Thanks,
> Anatoly