linux-kernel - Re: [PATCHv3 00/14] x86/tdx: Add kexec support

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Date:   Tue, 21 Nov 2023 11:43:21 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Baoquan He <bhe@...hat.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, ltao@...hat.com,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Jun Nakajima <jun.nakajima@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "Kalra, Ashish" <ashish.kalra@....com>,
        Sean Christopherson <seanjc@...gle.com>,
        "Huang, Kai" <kai.huang@...el.com>, kexec@...ts.infradead.org,
        linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3 00/14] x86/tdx: Add kexec support

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

> 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