Re: [Qemu-devel] [PATCH] RFC: vmcoreinfo device

[Marc-André Lureau]

Hi

On Mon, May 29, 2017 at 4:44 PM Igor Mammedov <address@hidden> wrote:

> On Fri, 26 May 2017 13:59:09 +0000
> Marc-André Lureau <address@hidden> wrote:
>
> > Hi
> >
> > On Thu, May 4, 2017 at 5:41 PM Igor Mammedov <address@hidden>
> wrote:
> >
> > > On Tue, 02 May 2017 19:03:15 +0000
> > > Marc-André Lureau <address@hidden> wrote:
> > >
> > > > Hi
> > > >
> > > > On Tue, May 2, 2017 at 11:17 AM Igor Mammedov <address@hidden>
> > > wrote:
> > > >
> > > > > On Fri, 28 Apr 2017 14:28:38 +0000
> > > > > Marc-André Lureau <address@hidden> wrote:
> > > > >
> > > > > > Hi
> > > > > >
> > > > > > On Fri, Apr 28, 2017 at 6:12 PM Ladi Prosek <address@hidden>
> > > wrote:
> > > > > >
> > > > > > > On Mon, Apr 24, 2017 at 3:03 PM, Marc-André Lureau
> > > > > > > <address@hidden> wrote:
> > > > > > > > The VM coreinfo (vmcoreinfo) device is an emulated device
> which
> > > > > > > > exposes a 4k memory range to the guest to store various
> > > informations
> > > > > > > > useful to debug the guest OS. (it is greatly inspired by the
> > > VMGENID
> > > > > > > > device implementation)
> > > > > > > >
> > > > > > > > This is an early-boot alternative to the qemu-ga VMDUMP_INFO
> > > event
> > > > > > > > proposed in "[PATCH 00/21] WIP: dump: add kaslr support".
> > > > > > > >
> > > > > > > > If deemed more appropriate, we can consider writing to fw_cfg
> > > > > directly
> > > > > > > > instead of guest memory, now that qemu 2.9 supports it again.
> > > > > > > >
> > > > > > > > The proof-of-concept kernel module:
> > > > > > > >
> > > https://github.com/elmarco/vmgenid-test/blob/master/qemuvmci-test.c
> > > > > > >
> > > > > > > Here's a proof-of-concept Windows driver:
> > > > > > >
> > > > > > >
> > > > >
> > >
> https://github.com/ladipro/kvm-guest-drivers-windows/tree/vmcoreinfo/vmcoreinfo
> > > > > > >
> > > > > > > I just wanted to be sure that it's possible to evaluate the
> ADDR
> > > > > > > method in Windows.
> > > > > > >
> > > > > > > From a practical point of view it is unfortunate that this
> would
> > > be a
> > > > > > > completely new device. For Windows guests it means another
> driver
> > > > > > > binary and all the overhead associated with deploying it on
> VMs.
> > > Would
> > > > > > > it be too crazy to add this functionality to the pvpanic
> device?
> > > The
> > > > > > > mechanics could stay the same but it would be done under the
> > > existing
> > > > > > > ACPI\QEMU0001 device.
> > > > > > >
> > > > > >
> > > > > > pvpanic is under _SB.PCI0.ISA, that could be problematic
> > > > > >
> > > > > > and _STA is a name field.
> > > > > >
> > > > > > Someone with more experience with ACPI could tell us if that make
> > > sense
> > > > > to
> > > > > > merge both and how.
> > > > > >
> > > > > > Can't you handle 2 ACPI devices in the same windows driver
> instead?
> > > > > we use QEMU0001 to reserve IO ports for pvpanic device,
> > > > > ASL wise there shouldn't problems with adding _ADDR method to it
> > > > >
> > > > > but then we probably should fold vmcoreinfo into pvpanic device
> > > > > as well (QEMU and linux driver)
> > > > >
> > > > >
> > > > pvpanic is x86-only afaict.
> > > There is nothing that forces it to be x86 specific (beside being ISA
> > > device),
> > > ARM also can benefit from/use pvpanic if you make it pci device or just
> > > plain
> > > Device.
> > >
> >
> > Could someone advise on a recommended solution here?
> >
> > Should we make a PCI variant of pvpanic and add the proposed vmcoreinfo
> > ACPI/mem to it ?
> >
> > Tbh, I think I prefer to have seperate devices since they work
> differently
> > and vmcoreinfo doesn't require any bus device.
> Considering pvpanic and vmcore are closely related, I'd prefer
> it being one device. But I won't insist on it.
>
> Also instead of PCI device, I'd use plain Device as vmgenid does,
> that would leave open question how to make legacy ISA based pvpanic
> on top of it in case both are merged.
>
>
Can we instead try to fit pvpanic functionality in the proposed vmcoreinfo
device? This could be done in a future revision of the device. This way we
don't have to deal with legacy ISA, and can make pvpanic functionality more
portable.

Tbh, I have no idea how to do the merging of the legacy ISA pvpanic with
vmcoreinfo without breaking things, nor do I have the motivation to do so.

More comments welcome (I would like to resend the patch as non-rfc this
time, I hope we can make it in 2.10)

Thanks

-- 
Marc-André Lureau