Re: [Xen-devel] pvgrub2 is merged

[Vladimir 'Ï-coder/phcoder' Serbinenko <phcoder@xxxxxxxxx>]

On 19.12.2013 12:54, Stefano Stabellini wrote:
> On Wed, 18 Dec 2013, Vladimir 'Ï-coder/phcoder' Serbinenko wrote:
>> On 18.12.2013 20:39, Stefano Stabellini wrote:
>>> On Wed, 18 Dec 2013, Vladimir 'Ï-coder/phcoder' Serbinenko wrote:
>>>> On 17.12.2013 15:35, Fabio Fantoni wrote:
>>>>> Il 17/12/2013 15:10, Fabio Fantoni ha scritto:
>>>>>> Il 17/12/2013 15:08, Vladimir 'Ï-coder/phcoder' Serbinenko ha scritto:
>>>>>>>> Thanks.
>>>>>>>> Now there is another error, probably introduced by xenfb support:
>>>>>>>>
>>>>>>> doesn't look like related to xenfb. Is it 64-bit or PAE guest?
>>>>>>
>>>>>> 64 bit
>>>>>
>>>>> I did "git reset --hard" to commit "Remove grub_bios_interrupt on
>>>>> coreboot." and then I applied only
>>>>> "grub-core/lib/x86_64/xen/relocator.S: Fix hypercall ABI violation."
>>>>> commit.
>>>>> Now the Sid domU boot correctly, therefore the regression is caused by
>>>>> "xenfb" or "xen grants to v1" commit, should I find the exact commit
>>>>> that causes that problem or these informations are enough for you?
>>>>
>>>> It's because of vfb. Apparently vfb framebuffer stays mapped as rw even
>>>> after vfb shutdown
>>>> phcoder@debian:15:52:40:~/grub2$ sudo xenstore-ls
>>>> /local/domain/54/device/vfb
>>>> 0 = ""
>>>>  backend = "/local/domain/0/backend/vfb/54/0"
>>>>  backend-id = "0"
>>>>  state = "1"
>>>> phcoder@debian:15:52:51:~/grub2$ sudo xenstore-ls
>>>> /local/domain/0/backend/vfb/54/0
>>>> frontend = "/local/domain/54/device/vfb/0"
>>>> frontend-id = "54"
>>>> online = "1"
>>>> state = "2"
>>>> domain = "grub"
>>>> vnc = "1"
>>>> vnclisten = "127.0.0.1"
>>>> vncdisplay = "0"
>>>> vncunused = "1"
>>>> sdl = "0"
>>>> opengl = "0"
>>>> feature-resize = "1"
>>>> hotplug-status = "connected"
>>>>
>>>> When I do "dry vfb": do everything except writing vfb state problem
>>>> disappears. So my question would be:
>>>> - how can I inspect how backend maps framebuffer pages?
>>>
>>> There is only one xenfb backend: hw/display/xenfb.c in the QEMU source
>>> tree.
>>>
>>>
>>>> - Why does it map as rw and not ro? It doesn't need to write to 
>>>> framebuffer?
>>>
>>> Actually it is mapping it RO, see hw/display/xenfb.c:xenfb_map_fb
>>>
>> ./tools/qemu-xen-dir-remote/hw/xenfb.c:
>>     xenfb->pixels = xc_map_foreign_pages(xen_xc, xenfb->c.xendev.dom,
>>                                       PROT_READ | PROT_WRITE, fbmfns, 
>> xenfb->fbpages);
> 
> You are right, my bad.
> I did a quick test and it should be safe to modify it to PROT_READ only.
> 
> 
>>>> - How do I force it to drop the mapping?
>>>
>>> Theoretically QEMU should drop the mapping at disconnect time:
>>>
>>> hw/display/xenfb.c:fb_disconnect
>>>
>>>     /*
>>>      * FIXME: qemu can't un-init gfx display (yet?).
>>>      *   Replacing the framebuffer with anonymous shared memory
>>>      *   instead.  This releases the guest pages and keeps qemu happy.
>>>      */
>>>     fb->pixels = mmap(fb->pixels, fb->fbpages * XC_PAGE_SIZE,
>>>                       PROT_READ | PROT_WRITE, MAP_SHARED | MAP_ANON,
>>>                       -1, 0);
>>>
>> Could this fail?
> 
> Yes and we don't check for the return value (-1 in case of error). Well 
> spotted!
> Do you want to submit a patch to fix both issues or should I do it?
> 
I'm fine with you doing it.

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