Re: [Qemu-devel] RFC: guest-side retrieval of fw_cfg file

[Gabriel L. Somlo]

On Tue, Jul 14, 2015 at 10:43:46AM +0100, Richard W.M. Jones wrote:
> On Mon, Jul 13, 2015 at 04:09:37PM -0400, Gabriel L. Somlo wrote:
> > 3. I'm currently only handling x86 and I/O ports. I could drop the
> >    fw_cfg_dmi_whitelist and just check the signature, using mmio where
> >    appropriate, but I don't have a handy-dandy set of VMs for those
> >    architectures on which I could test. Wondering if that's something
> >    we should have before I officially try to submit this to the kernel,
> >    or whether it could wait for a second iteration.
> 
>   $ virt-builder --arch armv7l fedora-22
> or:
>   $ virt-builder --arch aarch64 fedora-22
> then:
>   $ virt-builder --get-kernel fedora-22.img
> 
> and then boot is using the right qemu command, probably something
> like:
> 
>   $ qemu-system-arm \
>       -M virt,accel=tcg \
>       -cpu cortex-a15 \
>       -kernel vmlinuz-4.0.4-301.fc22.armv7hl+lpae \
>       -initrd initramfs-4.0.4-301.fc22.armv7hl+lpae.img \
>       -append "console=ttyAMA0 root=/dev/vda3 ro" \
>       -drive file=fedora-22.img,if=none,id=hd \
>       -device virtio-blk-device,drive=hd \
>       -serial stdio
> 
> The root password is printed in virt-builder output.

OK, so I replaced my port i/o with mmio equivalents:

-#define FW_CFG_PORT_CTL  0x510
+#define FW_CFG_PORT_CTL  (void *)0x09020008

-#define FW_CFG_PORT_DATA 0x511
+#define FW_CFG_PORT_DATA (void *)0x09020000

-       outw(select, FW_CFG_PORT_CTL);
+       writew(select, FW_CFG_PORT_CTL);

-       inb(FW_CFG_PORT_DATA);
+       readb(FW_CFG_PORT_DATA);

-       insb(FW_CFG_PORT_DATA, buf, count);
+       readsb(FW_CFG_PORT_DATA, buf, count);

and managed to build the module for 4.0.4-301.fc22.armv7hl+lpae, but
when I attempt to insmod the resulting .ko, I get an oops:

"Unable to handle kernel paging request at virtual address 09020008"

I grabbed the control and data addresses from qemu's hw/arm/virt.c:

        a15memmap[VIRT_FW_CFG] is { 0x09020000, 0x0000000a }

and used the "fw_cfg_init_mem_wide(base + 8, base, 8)" call to guess
that CTL should be DATA + 8 :)

I'm probably missing something that'll turn out to be really obvious
in retrospect... :)

TIA for any clue,
--Gabriel