linux-kernel - Re: linux-next: build failure after merge of the kvm-arm tree

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Date: Thu, 22 Feb 2024 18:58:39 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: Marc Zyngier <maz@...nel.org>
Cc: Paolo Bonzini <pbonzini@...hat.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Joey Gouly <joey.gouly@....com>,
	Christoffer Dall <cdall@...columbia.edu>, KVM <kvm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Next Mailing List <linux-next@...r.kernel.org>
Subject: Re: linux-next: build failure after merge of the kvm-arm tree

On Thu, Feb 22, 2024 at 02:31:38PM +0000, Marc Zyngier wrote:
> On Thu, 22 Feb 2024 13:11:59 +0000,
> Paolo Bonzini <pbonzini@...hat.com> wrote:
> > 
> > On 2/22/24 12:40, Stephen Rothwell wrote:
> > >> This fails because https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/commit/?id=fdd867fe9b32
> > >> added new fields to that register (ID_AA64DFR1_EL1)
> > >> 
> > >> and commit b80b701d5a6 ("KVM: arm64: Snapshot all non-zero RES0/RES1 sysreg fields for later checking")
> > >> took a snapshot of the fields, so the RES0 (reserved 0) bits don't match anymore.
> > >> 
> > >> Not sure how to resolve it in the git branches though.
> > > 
> > > Thanks.  I will apply this patch to the merge of the kvm-arm tree from
> > > tomorrow (and at the end of today's tree).
> > 
> > Marc, Oliver, can you get a topic branch from Catalin and friends for
> > this sysreg patch, and apply the fixup directly to the kvm-arm branch
> > in the merge commit?
> > 
> > Not _necessary_, as I can always ask Linus to do the fixup, but
> > generally he prefers to have this sorted out by the maintainers if it
> > is detected by linux-next.
> 
> I think that's not the correct thing to do at this time. I should have
> timed the introduction of these checks a bit later, after the merge
> window.
> 
> But more to the point, the proposed patch is also not the best thing
> to merge, because it hides that there is a discrepancy between what
> the architecture describes, and what KVM knows. I really want to know
> about it, or it will be yet another bug that we wont detect easily.
> Specially for ID_AA64DFR*_EL1 which are a bloody mine-field.
> 
> So I'd rather we make the check optional, and we'll play catch up for
> a bit longer. Something like the patch below.
> 
> Oliver, do you mind queuing this ASAP (also pushed out to my dev
> branch)?
> 
> Thanks,
> 
> 	M.
> 
> From 85d861a6ca055c7681c826c580e7c90d74c26ac5 Mon Sep 17 00:00:00 2001
> From: Marc Zyngier <maz@...nel.org>
> Date: Thu, 22 Feb 2024 14:12:09 +0000
> Subject: [PATCH] KVM: arm64: Make build-time check of RES0/RES1 bits optional
> 
> In order to ease the transition towards a state of absolute
> paranoia where all RES0/RES1 bits gets checked against what
> KVM know of them, make the checks optional and garded by a
> config symbol (CONFIG_KVM_ARM64_RES_BITS_PARANOIA) default to n.
> 
> Signed-off-by: Marc Zyngier <maz@...nel.org>

Applied as commit 99101dda29e3 ("KVM: arm64: Make build-time check of
RES0/RES1 bits optional") on the kvmarm/next branch.

-- 
Thanks,
Oliver