linux-kernel - Re: [PATCH v8 2/7] kexec: define functions to map and unmap segments

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Message-ID: <Z75i31INh5DAfW+R@MiWiFi-R3L-srv>
Date: Wed, 26 Feb 2025 08:39:59 +0800
From: Baoquan He <bhe@...hat.com>
To: steven chen <chenste@...ux.microsoft.com>
Cc: zohar@...ux.ibm.com, stefanb@...ux.ibm.com,
	roberto.sassu@...weicloud.com, roberto.sassu@...wei.com,
	eric.snowberg@...cle.com, ebiederm@...ssion.com,
	paul@...l-moore.com, code@...icks.com, bauermann@...abnow.com,
	linux-integrity@...r.kernel.org, kexec@...ts.infradead.org,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
	madvenka@...ux.microsoft.com, nramas@...ux.microsoft.com,
	James.Bottomley@...senpartnership.com, vgoyal@...hat.com,
	dyoung@...hat.com
Subject: Re: [PATCH v8 2/7] kexec: define functions to map and unmap segments

On 02/25/25 at 10:35am, steven chen wrote:
> On 2/24/2025 4:18 PM, Baoquan He wrote:
> > On 02/24/25 at 03:05pm, steven chen wrote:
> > > On 2/23/2025 10:14 PM, Baoquan He wrote:
> > > > Hi Steve, Mimi,
> > > > 
> > > > On 02/18/25 at 02:54pm, steven chen wrote:
> > > > > Currently, the mechanism to map and unmap segments to the kimage
> > > > > structure is not available to the subsystems outside of kexec.  This
> > > > > functionality is needed when IMA is allocating the memory segments
> > > > > during kexec 'load' operation.  Implement functions to map and unmap
> > > > > segments to kimage.
> > > > I am done with the whole patchset understanding. My concern is if this
> > > > TPM PCRs content can be carried over through newly introduced KHO. I can
> > > > see that these patchset doesn't introduce too much new code changes,
> > > > while if many conponents need do this, kexec reboot will be patched all
> > > > over its body and become ugly and hard to maintain.
> > > > 
> > > > Please check Mike Rapoport's v4 patchset to see if IMA can register
> > > > itself to KHO and do somthing during 2nd kernel init to restore those
> > > > TPM PCRs content to make sure all measurement logs are read correctly.
> > > > [PATCH v4 00/14] kexec: introduce Kexec HandOver (KHO)
> > > > 
> > > > Thanks
> > > > Baoquan
> > > Hi Baoquan,
> > > 
> > > For IMA, it appears that there are no current issues with TPM PCRs after a
> > > kernel soft reboot.
> > I mean using KHO to hold in 1st kernel and restore the IMA log in 2nd
> > kernel.
> > 
> > > This patches is used to get currently missed IMA measurements during the
> > > kexec process copied to new kernel after the kernel soft reboot. I think
> > > it's ok to leave it at current location: it will be easy to maintain for
> > > IMA.
> > Yeah, but I am saying this patchset increase unnecessary code
> > complexity in kexec code maintaining.
> > 
> > > Overall, for these patches, do you see any major blockers for kexec?
> > > 
> > > If you have any specific concerns or need further details, please let me
> > > know.
> > I have no concerns for this patchset implementation itself, I saw you using
> > vmap to maping the possible scattered source pages smartly and taking
> > the mapped buffer pointers to update later duing kexec jumping. That's very
> > great and clever method. BUT I am concerned about the solution, if we
> > can make use of the existed way of KHO to implement it more simply. Could
> > you please do investigation?
> 
> Hi Baoquan,
> 
> I will conduct an investigation. Thank you for your comments.

Thanks a lot, Steven.