Re: vhost-user technical isssues

[Linhaifeng <haifeng.lin-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

On 2014/11/14 10:30, Tetsuya Mukawa wrote:
> Hi Lin,
> 
> (2014/11/13 15:30), Linhaifeng wrote:
>> On 2014/11/12 12:12, Tetsuya Mukawa wrote:
>>> Hi Xie,
>>>
>>> (2014/11/12 6:37), Xie, Huawei wrote:
>>>> Hi Tetsuya:
>>>> There are two major technical issues in my mind for vhost-user implementation.
>>>>
>>>> 1) memory region map
>>>> Vhost-user passes us file fd and offset for each memory region. Unfortunately the mmap offset is "very" wrong. I discovered this issue long time ago, and also found
>>>> that I couldn't mmap the huge page file even with correct offset(need double check).
>>>> Just now I find that people reported this issue on Nov 3.
>>>> [Qemu-devel] [PULL 27/29] vhost-user: fix mmap offset calculation
>>>> Anyway, I turned to the same idea used in our DPDK vhost-cuse: only use the fd for region(0) to map the  whole file.
>>>> I think we should use this way temporarily to support qemu-2.1 as it has that bug.
>>> I agree with you.
>>> Also we may have an issue about un-mapping file on hugetlbfs of linux.
>>> When I check munmap(), it seems 'size' need to be aligned by hugepage size.
>>> (I guess it may be a kernel bug. Might be fixed already.)
>>> Please add return value checking code for munmap().
>>> Still munmap() might be failed.
>>>
>> are you munmmap the region 0? region 0 is not need to mmap so not need to munmap too.
>>
>> I can munmap success with the other regions.
> Could you please let me know how many size do you specify when you
> munmap region1?
> 

2G (region->memory_size + region.memory->offset)

> I still fail to munmap region1.
> Here is a patch to vhost-user test of QEMU. Could you please check it?
> 
> ----------------------------------
> diff --git a/tests/vhost-user-test.c b/tests/vhost-user-test.c
> index 75fedf0..4e17910 100644
> --- a/tests/vhost-user-test.c
> +++ b/tests/vhost-user-test.c
> @@ -37,7 +37,7 @@
> #endif
> 
> #define QEMU_CMD_ACCEL " -machine accel=tcg"
> -#define QEMU_CMD_MEM " -m 512 -object
> memory-backend-file,id=mem,size=512M,"\
> +#define QEMU_CMD_MEM " -m 6000 -object
> memory-backend-file,id=mem,size=6000M,"\
> "mem-path=%s,share=on -numa node,memdev=mem"
> #define QEMU_CMD_CHR " -chardev socket,id=chr0,path=%s"
> #define QEMU_CMD_NETDEV " -netdev
> vhost-user,id=net0,chardev=chr0,vhostforce"
> @@ -221,14 +221,16 @@ static void read_guest_mem(void)
> 
> /* check for sanity */
> g_assert_cmpint(fds_num, >, 0);
> - g_assert_cmpint(fds_num, ==, memory.nregions);
> + //g_assert_cmpint(fds_num, ==, memory.nregions);
> 
> + fprintf(stderr, "%s(%d)\n", __func__, __LINE__);
> /* iterate all regions */
> for (i = 0; i < fds_num; i++) {
> + int ret = 0;
> 
> /* We'll check only the region statring at 0x0*/
> if (memory.regions[i].guest_phys_addr != 0x0) {
> - continue;
> + //continue;
> }

if (memory.regions[i].guest_phys_addr == 0x0) {
	close(fd);
	continue;
}

> 
> g_assert_cmpint(memory.regions[i].memory_size, >, 1024);
> @@ -237,6 +239,13 @@ static void read_guest_mem(void)
> 
> guest_mem = mmap(0, size, PROT_READ | PROT_WRITE,
> MAP_SHARED, fds[i], 0);
> + fprintf(stderr, "guest_phys_addr=%lu, memory_size=%lu, "
> + "userspace_addr=%lu, mmap_offset=%lu\n",
> + memory.regions[i].guest_phys_addr,
> + memory.regions[i].memory_size,
> + memory.regions[i].userspace_addr,
> + memory.regions[i].mmap_offset);
> + fprintf(stderr, "mmap=%p, size=%lu\n", guest_mem, size);
> 
> g_assert(guest_mem != MAP_FAILED);
> guest_mem += (memory.regions[i].mmap_offset / sizeof(*guest_mem));
> @@ -248,7 +257,20 @@ static void read_guest_mem(void)
> g_assert_cmpint(a, ==, b);
> }
> 
> - munmap(guest_mem, memory.regions[i].memory_size);
> + ret = munmap(guest_mem, memory.regions[i].memory_size);
> + fprintf(stderr, "munmap=%p, size=%lu, ret=%d\n",
> + guest_mem, memory.regions[i].memory_size, ret);
> + {
> + size_t hugepagesize;
> +
> + size = memory.regions[i].memory_size;
> + /* assume hugepage size is 1GB, try again */
> + hugepagesize = 1024 * 1024 * 1024;
> + size = (size + hugepagesize - 1) / hugepagesize * hugepagesize;
> + }
size should be same as mmap and
guest_mem -= (memory.regions[i].mmap_offset / sizeof(*guest_mem));
> + ret = munmap(guest_mem, size);
> + fprintf(stderr, "munmap=%p, size=%lu, ret=%d\n",
> + guest_mem, size, ret);
> }
> 
> g_assert_cmpint(1, ==, 1);
> ----------------------------------
> $ sudo QTEST_HUGETLBFS_PATH=/mnt/huge make check
> region=0, mmap=0x2aaac0000000, size=6291456000
> region=0, munmap=0x2aab80000000, size=3070230528, ret=-1 << failed
> region=0, munmap=0x2aab80000000, size=3221225472, ret=0
> region=1, mmap=0x2aab80000000, size=655360
> region=1, munmap=0x2aab80000000, size=655360, ret=-1 << failed
> region=1, munmap=0x2aab80000000, size=1073741824, ret=0
> 
> 
> Thanks,
> Tetsuya
> 
> .
> 

-- 
Regards,
Haifeng