Re: [Xen-devel] Is there any limitation on the firmware size in Xen?

[Gary Lin <glin@xxxxxxxx>]

On Wed, May 10, 2017 at 04:47:49PM +0100, Wei Liu wrote:
> On Wed, May 10, 2017 at 04:39:32PM +0100, Wei Liu wrote:
> > On Wed, May 10, 2017 at 08:29:35AM -0600, Charles Arnold wrote:
> > > I was asked the following question which I am posting to the list.
> > > 
> > > "
> > > My name is Gary Lin, and I am the maintainer of the OVMF package, a UEFI
> > > implementation for the virtual machines.
> > > 
> > > Recently, I was testing an upstream patchset[*] and encountered some
> > > problems in Xen. Maybe you can help me or give me some hints.
> > > 
> > > To be short, the edk2/ovmf upstream is going to increase the firmware
> > > size from 2MB to 4MB to fulfill windows HCK, and we have to test
> > > different types of VM to make sure the patchset really work. When I was
> > > using the 2MB build, my Xen HVM worked as expected and showed the boot
> > > menu. However, if I use the 4MB build, I got something like this from
> > > "xl dmesg":
> > > 
> > > (d32)  - CPU0 ... 39-bit phys ... fixed MTRRs ... var MTRRs [1/8] ... 
> > > done.
> > > (d32) Testing HVM environment:
> > > (d32)  - REP INSB across page boundaries ... passed
> > > (d32)  - GS base MSRs and SWAPGS ... passed
> > > (d32) Passed 2 of 2 tests
> > > (d32) Writing SMBIOS tables ...
> > > (d32) Loading OVMF ...
> > > (d32) no BIOS ROM image found
> > > (d32) *** HVMLoader bug at hvmloader.c:389
> > > (d32) *** HVMLoader crashed.
> > > 
> > > I tried to trace the code and found that in 
> > > libxl__load_hvm_firmware_module()
> > > in tools/libxl/libxl_dom.c actully loaded the file and 
> > > add_module_to_list()
> > > in tools/libxc/xc_dom_x86.c was loading a firmware "module" with 4194304
> > > bytes. However, when hvmloader loaded "bios_module" with 
> > > get_module_entry(),
> > > modlist is NULL. It seems the firmware data was removed for some reason.
> > > 
> > > Here are my questions:
> > > 
> > > 1. Is there any limitation on the firmware size in Xen?
> > > 
> > 
> > OVMF is loaded into 4GB - ovmf_size. There shouldn't be limitation in
> > that regard. HVMloader should be happy with that address range.
> 
> Oh wait, it hasn't gone that far into loading OVMF.
> 
> IT would be useful, as a starting point, to go through modlist, print
> out and compare module loading addresses and lengths from both libxc and
> hvmloader.
> 

I printed the address and contents of hvm_start_info in get_module_entry().
Here is the result.

4MB build:

(d39) get_module_entry info 0x588000
(d39) info->magic         0x0
(d39) info->version       0x0
(d39) info->flags         0x0
(d39) info->nr_modules    0x0
(d39) info->modlist_paddr 0x0
(d39) info->cmdline_paddr 0x0
(d39) info->rsdp_paddr    0x0

Obviously, it's corrupted since magic is 0.

2MB build:

(d40) get_module_entry info 0x388000
(d40) info->magic         0x336ec578
(d40) info->version       0x0
(d40) info->flags         0x0
(d40) info->nr_modules    0x1
(d40) info->modlist_paddr 0x388028
(d40) info->cmdline_paddr 0x0
(d40) info->rsdp_paddr    0x0

This looks alright and grub2 menu showed.

It seems the starting address increased 2MB, and I wonder if this
matters.

Thanks,

Gary Lin

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