Re: [SeaBIOS] Qemu-kvm VM halt at allocate VGA stack when continuously reset VM

[Xulei (Stone)]

> > On Sat, Nov 28, 2015 at 07:12:47AM +0000, Xulei (Stone) wrote:
> > > Hi,
> > > Recently, i use a script to continuously reset a VM and
> > > i found my VM frequently halts at "Attempting to allocate
> > > VGA stack via pmm call". After analyzing, i think it may
> > > be a problem of SeaBIOS.
> > >
> > > From the log(attached below), we can see handle_post()
> > > executes twice and this makes the destination address of
> > > "Relocating init" change when the 2nd reset command comes.
> > > This also influences on the source address of "Copying MPTABLE".
> > > At last, the VM will be stuck at attempting to allocate VGA
> > > stack via pmm call.
> > >
> > > Could you offer me a solution to fix this problem?
> > >
> > > ==============bad SeaBIOS log======
> > > SeaBIOS (version rel-1.8.1-0-g4adadbd-20151127_220019-UVP)
> > > No Xen hypervisor found.
> > > Running on QEMU (i440fx)
> > > Running on KVM
> > > RamSize: 0xc0000000 [cmos]
> > > Now vcpu cpu_id = 0                                          <<========= i add
> > > Static seabios entry times =1                                <<========= i add
> > > Relocating init from 0x000dbb30 to 0xbffad2c0 (size 76928)
> > > Found QEMU fw_cfg
> > > SeaBIOS (version rel-1.8.1-0-g4adadbd-20151127_220019-UVP)   <<=========  handle_post() execute again?
> >
> > If seabios resets before it sets HaveRunPost then it probably wont
> > work well, as it will rerun the POST code without resetting the global
> > variables it has modified.
> >
> > Unfortunately, it's not clear to me that we can simply move the
> > setting of HaveRunPost to an earlier point, as the handle_resume()
> > code would need to be audited to ensure it can run even if POST hasn't
> > completed.
>
> I move HaveRunPost = 1 in the very early point of POST phase (begin
> at handle_post()), so that when the 2nd reset comes, HaveRunPost is
> already 1 which makes entry_post jmps to handle_resume() instead of
> handle_post(). As we know, handle_resume() will reset all global variables.
>
> Can you tell me is this solution ok? or, does this have some side effects?

Sorry, i've tested and this seems not work. Let HaveRunPost = 1 at begin
of handle_post(), will lead the VM to loop forever in the resume phase.
It seems the memcpy() in qemu_prep_reset()can not clear HaveRunPost at
this time.

Ah! I'm confused! I don't know where is the right place to let HaveRunPost = 1?
> > So, it looks like a fix for this will take some further analysis.
> >
> > -Kevin