On Tue, Dec 06, 2016 at 06:15:34PM -0800, Ben Warren wrote:
> Hi Michael,
>
> I’m well on my way to implementing this, but I am really new to the QEMU code
> base and am struggling with some concepts. Please see below:
> > On Oct 5, 2016, at 6:29 PM, Michael S. Tsirkin <m...@redhat.com> wrote:
> >
> > On Tue, Oct 04, 2016 at 03:51:40PM -0700, Ed Swierk wrote:
> >> On Thu, Sep 15, 2016 at 5:36 PM, Michael S. Tsirkin <m...@redhat.com>
> >> wrote:
> >>> On Thu, Sep 15, 2016 at 05:23:28PM -0700, Ed Swierk wrote:
> >>>> I'm wondering what it will take to finish up work on vmgenid.
> >>>>
> >>>> https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg05599.html
> >>>
> >>> We have ACPI_BUILD_TPMLOG_FILE in tree now and I think it could be
> >>> allocated in a similar way.
> >>> Integrate patch "fw-cfg: support writeable blobs" to communicate the
> >>> allocated address back to QEMU.
> >>
> >> Starting with Igor's last version at
> >> https://github.com/imammedo/qemu/commits/vmgen_wip , it's not clear to
> >> me which changes need to be ported, which changes are obsoleted by
> >> your new fw-cfg stuff and/or upstream churn in ACPI, device
> >> properties, etc. In particular ACPI is still a total mystery to me,
> >> though passing a single address from guest to host can't be that hard,
> >> can it?
> >>
> >> Any clues would be appreciated.
> >>
> >> --Ed
> >
> > It might be best to just re-start from the beginning.
> > So the idea is that ACPI should be about supplying the address
> > to guest. To supply address to host we'll use fw cfg.
> > This would be new I think:
> >
> > - add support for writeable fw cfg blobs
> patch applied
> > - add linker/loader command to write address of a blob into
> > such a fw cfg file
> > - add a new file used for vm gen id, use loader command above
> > to pass the address of a blob allocated for it to host
> I don’t really understand the meaning of “file” in this context. It seems to
> be a way of specifying individual fw_cfg entries without explicitly giving an
> index, but is not something that is visible in either the host or guest file
> system. Is this about right? In my code I’m using “/etc/vmgenid”
yes
> As for the blob, I’m thinking this is where my main problem is. The
> ‘fw_cfg_add_*()’ functions take a data pointer but doesn’t seem to copy the
> data anywhere. We pass essentially a pointer via ACPI to the guest, so what
> it points to needs to be in an accessible region. I don’t get how to define
> the blob contents. There are command-line ‘fw-cfg’ options where you can
> specify a file, but it’s not clear to me how to use them. Maybe I reserve
> some IO memory or something?
Not sure I understand the question. fw cfg device will make
memory accessible to guest. Put the guest physical address there.
the address needs to be calculated by linker.
> > - whenever vm gen id changes, update file, if we have address
> > of blob update that as well
> Will do that once I understand the other parts
> > - use linker to patch address of blob into acpi as well
> > it needs to be in a separate ssdt at top level
> > otherwise it's hard to figure out the offset.
> I have this going into a separate SSDT and can decode it using iasl on the
> guest:
> —————
> [root@playground ~]# cat SSDT.dsl
> /*
> * Intel ACPI Component Architecture
> * AML/ASL+ Disassembler version 20150717-64
> * Copyright (c) 2000 - 2015 Intel Corporation
> *
> * Disassembling to symbolic ASL+ operators
> *
> * Disassembly of SSDT, Tue Dec 6 16:35:14 2016
> *
> * Original Table Header:
> * Signature "SSDT"
> * Length 0x0000007C (124)
> * Revision 0x01
> * Checksum 0x29
> * OEM ID "BOCHS "
> * OEM Table ID "VMGENID"
> * OEM Revision 0x00000001 (1)
> * Compiler ID "BXPC"
> * Compiler Version 0x00000001 (1)
> */
> DefinitionBlock ("SSDT.aml", "SSDT", 1, "BOCHS ", "VMGENID", 0x00000001)
> {
> Scope (_SB)
> {
> Device (VGEN)
> {
> Name (_HID, "QEMU0003") // _HID: Hardware ID
> Name (_CID, "VM_Gen_Counter") // _CID: Compatible ID
> Name (_DDN, "VM_Gen_Counter") // _DDN: DOS Device Name
> Name (ADDR, Package (0x02)
> {
> 0xE7AAD010,
> 0x559F
> })
> }
> }
> }
> —————
> The address you see is the address of the host memory where I have the GUID
> stored, so is obviously incorrect.
>
> >
> > This can be reused from one of the previus versions:
> > - command line, interrupts and commands to update vm gen id
> >
> I have these all applied and can set/get the GUID via the QMP shell, and can
> pass GUID via QEMU command line. As for parsing the input, I have it modeled
> as a device right on the sysbus. Is this how it should be done, or would I
> pass the GUID in via the ‘fw_cfg’ command-line options, or something else?
> It’s a bit problematic as-is because it depends on machine types that allow
> dynamic-sysbus.
> > I can help with acpi if all the rest is clear.
> >
>
>
> > --
> > MST
> >
> >
> Sorry for being so dense - I think once I get the main concepts the rest of
> this should be straightforward. I’m happy to post a patch of the current
> work if that would help. Thanks in advance for your help.
>
> —Ben
