On Sat, Jan 14, 2017 at 10:17:53PM -0800, Ben Warren wrote: > Hi Michael, > > > On Dec 10, 2016, at 7:28 PM, Michael S. Tsirkin <m...@redhat.com> wrote: > > 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. > > > I’m almost ready to submit a V2 of the patch set, but there’s still one issue > that I can’t figure out. From the guest, I can read the contents of the blob. > If I make a change to the contents of the blob (via QMP) the guest does not > see the changes. Is there something I need to do on the QEMU side to “push” > the updated fw_cfg contents to the guest? I’ve noticed this both when writing > a qtest for the feature, and also in a Linux kernel module I wrote that reads > the ACPI contents in a guest. > > thanks, > Ben
fw cfg entities are assumed to be immutable. This week I'll merge support for writeable fw cfg entries. I don't see why you want to change fw cfg transparently though - I think it should be like this - guest writes GPA into fw cfg - qemu writes gen id at this GPA -- MST