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

[Maran Wilson <maran.wilson@xxxxxxxxxx>]

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 =
> >              __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?
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.
-Maran

> > > 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.
>
> -boris

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