Re: [Qemu-devel] vhost-user: broken mem regions

[Damjan Marion (damarion)]

On 25 Jun 2014, at 15:53, Michael S. Tsirkin <address@hidden> wrote:

> On Wed, Jun 25, 2014 at 01:45:09PM +0000, Damjan Marion (damarion) wrote:
>> 
>> Michael,
>> 
>> there is another issue with commited vhost-user code.
> 
> I'm answering just this once, but I have a policy against
> answering off-list mail.
> Pls send follow-ups to the list.

ok, sorry, adding list...

> 
>> If there is bigger mem allocation (i.e. 4G or 6G of RAM) then
>> we have memory gap and then it happens that buffer pointer points to 
>> memory which is not mmaped. I already filled bug report:
>> 
>> https://bugs.launchpad.net/qemu/+bug/1333688
> 
> FYI I mostly ignore launchpad.
> Because of the unfortunate association with Ubuntu, most bugs
> there are distro-specific.
> 
>> Bellow is my proposed change to the code. Two things: 
>> - it will require changes on the user side also
> 
> why would it?
> format seems unchanged, right?

yes, but it will happen that multiple regions have same FD so call to mmap()
should look different, I’m still playing with this on user side...

> 
>> - not sure if qemu_get_ram_fd() is the best way to get FD
> 
> Paolo, what do you think?
> 
>> Any comments or better idea how to fix this?
>> 
>> Thanks,
>> 
>> Damjan
>> 
>> diff --git a/hw/virtio/vhost-user.c b/hw/virtio/vhost-user.c
>> index 0df6a93..89fe5c7 100644
>> --- a/hw/virtio/vhost-user.c
>> +++ b/hw/virtio/vhost-user.c
>> @@ -14,6 +14,7 @@
>> #include "sysemu/kvm.h"
>> #include "qemu/error-report.h"
>> #include "qemu/sockets.h"
>> +#include "exec/ram_addr.h"
>> 
>> #include <fcntl.h>
>> #include <unistd.h>
>> @@ -183,10 +184,10 @@ static int vhost_user_call(struct vhost_dev *dev, 
>> unsigned long int request,
>> {
>>     VhostUserMsg msg;
>>     VhostUserRequest msg_request;
>> -    RAMBlock *block = 0;
>>     struct vhost_vring_file *file = 0;
>>     int need_reply = 0;
>>     int fds[VHOST_MEMORY_MAX_NREGIONS];
>> +    int i, fd;
>>     size_t fd_num = 0;
>> 
>>     assert(dev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER);
>> @@ -212,14 +213,14 @@ static int vhost_user_call(struct vhost_dev *dev, 
>> unsigned long int request,
>>         break;
>> 
>>     case VHOST_SET_MEM_TABLE:
>> -        QTAILQ_FOREACH(block, &ram_list.blocks, next)
>> -        {
>> -            if (block->fd > 0) {
>> -                msg.memory.regions[fd_num].userspace_addr =
>> -                    (uintptr_t) block->host;
>> -                msg.memory.regions[fd_num].memory_size = block->length;
>> -                msg.memory.regions[fd_num].guest_phys_addr = block->offset;
>> -                fds[fd_num++] = block->fd;
>> +        for (i = 0; i < dev->mem->nregions; ++i) {
>> +            struct vhost_memory_region *reg = dev->mem->regions + i;
>> +            fd = qemu_get_ram_fd(reg->guest_phys_addr);
>> +            if (fd > 0) {
>> +                msg.memory.regions[fd_num].userspace_addr = 
>> reg->userspace_addr;
>> +                msg.memory.regions[fd_num].memory_size  = reg->memory_size;
>> +                msg.memory.regions[fd_num].guest_phys_addr = 
>> reg->memory_size;
>> +                fds[fd_num++] = fd;
>>             }
>>         }
>>