[PATCHv5 0/8] arm64: zboot support

[Dave Young]

Hi Pingfan,

On Thu, 20 Jul 2023 at 10:05, Pingfan Liu <piliu at redhat.com> wrote:
>
> Hi Dave,
>
> Thanks for your insight. Please see the comments inline below.
>
> On Wed, Jul 19, 2023 at 11:00 AM Dave Young <dyoung at redhat.com> wrote:
> >
> > Hi Pingfan, Simon,
> >
> > On 07/17/23 at 09:07pm, Pingfan Liu wrote:
> > > As more complicated capsule kernel format occurs like zboot, where the
> > > compressed kernel is stored as a payload. The straight forward
> > > decompression can not meet the demand.
> > >
> > > As the first step, on aarch64, reading in the kernel file in a probe
> > > method and decide how to unfold the content by the method itself.
> > >
> > > This series introduce a new image probe interface probe2(), which
> > > returns three factors: kernel buffer, kernel size and kernel fd through
> > > a struct parsed_info.
> > > -1. the parsed kernel_buf should be returned so that it can be used by
> > > the image load method later.
> > > -2. the final fd passed to sys_kexec_file_load, since aarch64 kernel can
> > > only work with Image format, the outer payload should be stripped and a
> > > temporary file of Image should be created.
> >
> > I took a look at the Image.gz file load code, the current code can be
> > simplified with passing a fd directly instead of creating temp files via
> > memfd_create with the already decompressed kernel_buf.
> >
> > The current file load is like below:
> >
> > do_kexec_file_load():
> >   1.slurp_decompress_file
> >     2. probe
> >       3. load
> >         4. kexec_file_load
> >
> > In step 1, the Image.gz has been decompressed to kernel_buf, so just
> > create a virtual memfd copy to it, then save the virtual fd for step 4
> > use.
> >
> > Otherwise in step 2 it is some sanity checking, step 3 is setting
> > something else eg. initrd_fd, cmdline. With the changes below Image and
> > Image.gz will share same code. I think you can add the zboot
> > detection/checking code in the Image probe, load functions, with a new
> > info->kernel_fd, you can decompress the zboot kernel_buf and save to
> > another virtual memfd, and set to the info->kernel_fd.  Then in step 4
> > the kexec_file_load can just use it.
> >
>
> This only results in a minor change in the interface, not like mine. I
> prefer this method.
>
> > The kernel_buf itself is only used for sanity checking of the formats,
> > kernel only needs a file fd, so I think it should be fine and easier
> > than the original ways.
> >
>
> Overall, this new method minimally affects the function interface, in
> addition to the code simplification.
> I will try to take it in the next version.
>
Ok, great.  Btw, it would be ideal if some of the pez_prepare work can
be done early before the slurp_decompress_file in
do_kexec_file_load(), then it could be just arch independent :)

Thanks
Dave