[PATCHv3 00/14] x86/tdx: Add kexec support

[Tao Liu]

Hi Kirill,

On Tue, Nov 21, 2023 at 4:43 PM Kirill A. Shutemov
<kirill.shutemov at linux.intel.com> wrote:
>
> On Tue, Nov 21, 2023 at 02:41:08PM +0800, Baoquan He wrote:
> > > >
> > > > Still failed. And I found the normal reboot does't work either. I will
> > > > do more testing tomorrow, e.g use the tdx-tools's own rhel9 kernel
> > > > config and rebuild, and update host kernel too.
> >
> > I did more tests, resuls are summarized as below:
> >
> > 1) kexec reboot works, but always fallback to 1 cpu even though multiple
> > cpus are specified;
>
> That's expected. Until you have new BIOS. See below.
>
> > 2) kdump kernel need more crashkernel memory to boot up,
> >    crashkernel=512M works well in our case.
>
> I guess it is due to SWIOTLB memory which requres at least 64M.
>
> >  But it failed in vmcore
> >    saving process, either makedumpfile or cp can't access the 1st
> >    kernel's old memory;
>
> Will look into it.
>
> > 3) Normal reboot always failed;
>
> It is expected. TD vCPUs are not resettable. So we need to destroy TD and
> construct a new one to emulate "reboot".
>
> I guess we can try to add some glue on QEMU side to make reboot more
> seamless.
>
> > My colleague Tao helped to double check this, he got the same testing result.
> > Plesae
> > 1) what can we do to enable the multiple cpu support for kexec reboot?
>
> You would need a patched BIOS image. I've hacked one[1] for my testing.
> But it only works if kernel runs in 4-level paging mode (specify no5lvl in
> kernel command line).
>
> BIOS folks work on proper patch, but it is not ready yet.
>
> [1] https://gist.github.com/kiryl/e1dc1719e0c990b3ceee5d8de8dbf332
>
Thanks a lot for providing the BIOS patch. One more question, is the
patched BIOS image for the host physical machine or for the tdx guest
vm?

Thanks,
Tao Liu

> > 2) anything missing to allow makedumpfile/cp access 1st kernel's memory?
>
> It worked before for us, but I have not checked for a while.
>
> I expected you've dropped my "if (crash) return;" debug patch I asked you
> to tested before, right? If not, failure is expected.
>
> > 3) not sure if this is particular case on the system we tested on.
>
> --
>   Kiryl Shutsemau / Kirill A. Shutemov
>
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