On Fri, 2017-11-03 at 13:49 +0000, Jean-Philippe Brucker wrote:
On 02/11/17 15:50, Gerd Hoffmann wrote:
Queues have 256 entries on kvmtool, support that. Needs more memory for virtqueues now. But with the move to 32bit drivers for virtio this should not be much of an issue any more.
Known problems (probably kvmtool bugs): * Must bump to 260 entries to make things actually work, otherwise kvmtool segfaults. Oops.
You mean setting MAX_QUEUE_NUM to 256 instead of 260 in seabios causes a kvmtool crash?
yes.
Do you have any more detail on the segfault?
Ok, lets have a look with gdb ...
Program received signal SIGSEGV, Segmentation fault. [Switching to Thread 0x7f81caf3c700 (LWP 20234)] virt_queue__get_head_iov (vq=vq@entry=0x7f82576be0a0, iov=iov@entry=0x7 f826770aae0, out=out@entry=0x7f826770bae0, in=in@entry=0x7f826770bae2, head=65104, kvm=kvm@entry=0x246eee0) at virtio/core.c:105 105 *out = *in = 0; (gdb) bt #0 0x000000000040c91b in virt_queue__get_head_iov (vq=vq@entry=0x7f825 76be0a0, iov=iov@entry=0x7f826770aae0, out=out@entry=0x7f826770bae0, in =in@entry=0x7f826770bae2, head=65104, kvm=kvm@entry=0x246eee0) at virtio/core.c:105 #1 0x000000000040bbf7 in virtio_blk_thread (bdev=0x7f82576be010, vq=0x7f82576be0a0, kvm=0x246eee0) at virtio/blk.c:134 #2 0x000000000040bbf7 in virtio_blk_thread (dev=0x7f82576be010) at virtio/blk.c:208 #3 0x00007f82571c6e25 in start_thread () at /lib64/libpthread.so.0 #4 0x00007f82543b134d in clone () at /lib64/libc.so.6 (gdb) print *vq $1 = {vring = {num = 256, desc = 0x7f824cf3e000, avail = 0x7f824cf3f000, used = 0x7f824cf40000}, pfn = 524285, last_avail_idx = 263, last_used_signalled = 1, endian = 1}
last_avail_idx looks bogus ...
Since seabios doesn't use the event indexes, this would lead to missing signals, but not a segfault.
seabios polls anyway, so it doesn't need signals.
* Linux kernel doesn't find virtio-blk devices after seabios initialized them. virtio device reset not working properly?
No, reset isn't implemented at all... A lot of work is required to properly clear the state and threads of each device.
Hmm. That is required for any kind of boot loader support though.
/me wonders what the kvmtool --firmware switch is good for then if a direct kernel boot is apparently the only thing which actually works.
cheers, Gerd