Re: [Qemu-devel] [RFC v2 0/4] QEMU changes to do PVH boot

[Stefano Garzarella]

Hi Liam,

On Tue, Jan 8, 2019 at 3:47 PM Liam Merwick <address@hidden> wrote:
> QEMU sets the hvm_modlist_entry in load_linux() after the call to
> load_elfboot() and then qboot loads it in boot_pvh_from_fw_cfg()
>
> But the current PVH patches don't handle initrd (they have
> start_info.nr_modules == 1).

Looking in the linux kernel (arch/x86/platform/pvh/enlighten.c) I saw:
    /* The first module is always ramdisk. */
    if (pvh_start_info.nr_modules) {
        struct hvm_modlist_entry *modaddr =
            __va(pvh_start_info.modlist_paddr);
        pvh_bootparams.hdr.ramdisk_image = modaddr->paddr;
        pvh_bootparams.hdr.ramdisk_size = modaddr->size;
    }

So, putting start_info.nr_modules = 1, means that the first
hvm_modlist_entry should have the ramdisk paddr and size. Is it
correct?


>
> During (or after) the call to load_elfboot() it looks like we'd need to
> do something like what load_multiboot() does below (along with the
> associated initialisation)
>
> 400     fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_ADDR, ADDR_MBI);
> 401     fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_SIZE, sizeof(bootinfo));
> 402     fw_cfg_add_bytes(fw_cfg, FW_CFG_INITRD_DATA, mb_bootinfo_data,
> 403                      sizeof(bootinfo));
>

In this case I think they used the FW_CFG_INITRD_* to pass bootinfo
varibales to the guest, maybe we could add something like what
linux_load() does:

    /* load initrd */
    if (initrd_filename) {
        ...
        initrd_addr = (initrd_max-initrd_size) & ~4095;

        fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_ADDR, initrd_addr);
        fw_cfg_add_i32(fw_cfg, FW_CFG_INITRD_SIZE, initrd_size);
        fw_cfg_add_bytes(fw_cfg, FW_CFG_INITRD_DATA, initrd_data, initrd_size);
        ...
    }

Then we can load the initrd in qboot or in the optionrom that I'm writing.

What do you think?

Thanks,
Stefano

> I'm checking to see if that has any implications for the kernel side.
>
> Regards,
> Liam
>


-- 
Stefano Garzarella
Red Hat