Re: [PATCH] tools/xg: increase LZMA_BLOCK_SIZE for uncompressing the kernel

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Tue, Oct 08, 2024 at 11:32:23PM +0200, Marek Marczykowski-Górecki wrote:
> Linux 6.12-rc2 fails to decompress with the current 128MiB, contrary to
> the code comment. It results in a failure like this:
> 
>     domainbuilder: detail: xc_dom_kernel_file: 
> filename="/var/lib/qubes/vm-kernels/6.12-rc2-1.1.fc37/vmlinuz"
>     domainbuilder: detail: xc_dom_malloc_filemap    : 12104 kB
>     domainbuilder: detail: xc_dom_module_file: 
> filename="/var/lib/qubes/vm-kernels/6.12-rc2-1.1.fc37/initramfs"
>     domainbuilder: detail: xc_dom_malloc_filemap    : 7711 kB
>     domainbuilder: detail: xc_dom_boot_xen_init: ver 4.19, caps 
> xen-3.0-x86_64 hvm-3.0-x86_32 hvm-3.0-x86_32p hvm-3.0-x86_64
>     domainbuilder: detail: xc_dom_parse_image: called
>     domainbuilder: detail: xc_dom_find_loader: trying multiboot-binary loader 
> ...
>     domainbuilder: detail: loader probe failed
>     domainbuilder: detail: xc_dom_find_loader: trying HVM-generic loader ...
>     domainbuilder: detail: loader probe failed
>     domainbuilder: detail: xc_dom_find_loader: trying Linux bzImage loader ...
>     domainbuilder: detail: _xc_try_lzma_decode: XZ decompression error: 
> Memory usage limit reached
>     xc: error: panic: xg_dom_bzimageloader.c:761: xc_dom_probe_bzimage_kernel 
> unable to XZ decompress kernel: Invalid kernel
>     domainbuilder: detail: loader probe failed
>     domainbuilder: detail: xc_dom_find_loader: trying ELF-generic loader ...
>     domainbuilder: detail: loader probe failed
>     xc: error: panic: xg_dom_core.c:689: xc_dom_find_loader: no loader found: 
> Invalid kernel
>     libxl: error: libxl_dom.c:566:libxl__build_dom: xc_dom_parse_image failed
> 
> The important part: XZ decompression error: Memory usage limit reached
> 
> This looks to be related to the following change in Linux:
> 8653c909922743bceb4800e5cc26087208c9e0e6 ("xz: use 128 MiB dictionary and 
> force single-threaded mode")
> 
> Fix this by increasing the block size to 256MiB. And remove the
> misleading comment (from lack of better ideas).
> 
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

I assumed I already RB this, but it seems not.

Could we get an Ack from the tools or libs maintainer for this to go
in?  It's not the best solution, but we need to get this sorted in
time for 4.20, and backport to stable branches.

Thanks, Roger.