[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

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

On 1/9/2019 11:53 AM, Boris Ostrovsky wrote:
On 1/9/19 6:53 AM, Stefano Garzarella wrote:
Hi Liam,

On Tue, Jan 8, 2019 at 3:47 PM Liam Merwick <liam.merwick@xxxxxxxxxx> 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 =
         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

That's my understanding.

I think what's missing, is that we just need Qemu or qboot/seabios to properly populate the pvh_start_info.modlist_paddr with the address (as usable by the guest) of the hvm_modlist_entry which correctly defines the details of the initrd that has already been loaded into memory that is accessible by the guest.


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?

Why not specify this in pvh_start_info? This will be much faster for
everyone, no need to go through fw_cfg.


Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.