linux-kernel - Re: [PATCH v15 0/6] arm64: Reorganize the unwinder and implement stack trace reliability checks

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Date:   Sun, 26 Jun 2022 10:18:44 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
Cc:     Will Deacon <will@...nel.org>, broonie@...nel.org,
        jpoimboe@...hat.com, ardb@...nel.org, nobuta.keiya@...itsu.com,
        sjitindarsingh@...il.com, catalin.marinas@....com,
        jamorris@...ux.microsoft.com, linux-arm-kernel@...ts.infradead.org,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        maz@...nel.org, Kalesh Singh <kaleshsingh@...gle.com>
Subject: Re: [PATCH v15 0/6] arm64: Reorganize the unwinder and implement
 stack trace reliability checks

On Fri, Jun 24, 2022 at 12:19:01AM -0500, Madhavan T. Venkataraman wrote:
> 
> 
> On 6/23/22 12:32, Will Deacon wrote:
> > On Fri, Jun 17, 2022 at 04:07:11PM -0500, madvenka@...ux.microsoft.com wrote:
> >> From: "Madhavan T. Venkataraman" <madvenka@...ux.microsoft.com>
> >>
> >> I have synced this patch series to v5.19-rc2.
> >> I have also removed the following patch.
> >>
> >> 	[PATCH v14 7/7] arm64: Select HAVE_RELIABLE_STACKTRACE
> >>
> >> as HAVE_RELIABLE_STACKTRACE depends on STACK_VALIDATION which is not present
> >> yet. This patch will be added in the future once Objtool is enhanced to
> >> provide stack validation in some form.
> > 
> > Given that it's not at all obvious that we're going to end up using objtool
> > for arm64, does this patch series gain us anything in isolation?
> > 
> 
> BTW, I have synced my patchset to 5.19-rc2 and sent it as v15.
> 
> So, to answer your question, patches 1 thru 3 in v15 are still useful even if we don't
> consider reliable stacktrace. These patches reorganize the unwinder code based on
> comments from both Mark Rutland and Mark Brown. Mark Brown has already OKed them.
> If Mark Rutland OKes them, we should upstream them.

Sorry for the delay; I have been rather swamped recently and haven't had the
time to give this the time it needs.

I'm happy with patches 1 and 2, and I've acked those in case Will wants to pick
them.

Kalesh (cc'd) is working to share the unwinder code with hyp, and I think that
we need to take a step back and consider how we can make the design work
cleanly with that. I'd had a go at prototyping making the unwinder more data
driven, but I haven't come up with something satisfactory so far.

It would be good if you could look at / comment on each others series.

Thanks,
Mark.

> 
> I can drop patches 4 thru 6. Actually, the objtool patch series that I have
> sent separately for supporting livepatch already addresses reliability. So, if that
> gets reviewed and accepted, we don't even need patches 4 thru 6.
> 
> If you are OK with that, I can resend v16 with just patches 1 thru 3. Let me know.
> 
> Madhavan
>