Re: [Xen-devel] pvgrub2 is merged

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

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);

> 
>> - 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?

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