From: David Brazdil <dbrazdil@google.com>
To: Will Deacon <will@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
Christoph Lameter <cl@linux.com>, Arnd Bergmann <arnd@arndb.de>,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, kvmarm@lists.cs.columbia.edu,
linux-arch@vger.kernel.org, kernel-team@android.com
Subject: Re: [PATCH v2 00/10] Independent per-CPU data section for nVHE
Date: Wed, 16 Sep 2020 12:54:04 +0100 [thread overview]
Message-ID: <20200916115404.rhv4dkyjz35e4x25@google.com> (raw)
In-Reply-To: <20200914174008.GA25238@willie-the-truck>
Hi Will,
On Mon, Sep 14, 2020 at 06:40:09PM +0100, Will Deacon wrote:
> Hi David,
>
> On Thu, Sep 03, 2020 at 11:17:02AM +0200, David Brazdil wrote:
> > Introduce '.hyp.data..percpu' as part of ongoing effort to make nVHE
> > hyp code self-contained and independent of the rest of the kernel.
> >
> > The series builds on top of the "Split off nVHE hyp code" series which
> > used objcopy to rename '.text' to '.hyp.text' and prefix all ELF
> > symbols with '__kvm_nvhe' for all object files under kvm/hyp/nvhe.
>
> I've been playing around with this series this afternoon, trying to see
> if we can reduce the coupling between the nVHE code and the core code. I've
> ended up with the diff below on top of your series, but I think it actually
> removes the need to change the core code at all. The idea is to collapse
> the percpu sections during prelink, and then we can just deal with the
> resulting data section a bit like we do for .hyp.text already.
>
> Have I missed something critical?
I was wondering whether this approach would be sufficient as well because of
the simplicity. We'd just need to be careful about correctly preserving the
semantics of the different .data..percpu..* sections.
For instance, I've noticed you make .hyp..data..percpu page-aligned rather than
cacheline-aligned. We need that for stage-2 unmapping but it also happens to
correctly align DEFINE_PER_CPU_PAGE_ALIGNED variables when collapsed into the
single hyp section. The reason why I ended up reusing the global macro was to
avoid introducing subtleties like that into the arm64 linker script. Do you
think it's a worthwhile trade off?
One place where this approach doesn't work is DEFINE_PER_CPU_FIRST. But I'm
guessing that's something we can live without.
I was also wondering about another approach - using the PERCPU_SECTION macro
unchanged in the hyp linker script. It would lay out a single .data..percpu and
we would then prefix it with .hyp and the symbols with __kvm_nvhe_ as with
everything else. WDYT? Haven't tried that yet, could be a naive idea.
Thanks for reviewing,
David
next prev parent reply other threads:[~2020-09-16 21:09 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-03 9:17 [PATCH v2 00/10] Independent per-CPU data section for nVHE David Brazdil
2020-09-03 9:17 ` [PATCH v2 01/10] Macros to override naming of percpu symbols and sections David Brazdil
2020-09-03 9:17 ` [PATCH v2 02/10] kvm: arm64: Partially link nVHE hyp code, simplify HYPCOPY David Brazdil
2020-09-10 9:54 ` Andrew Scull
2020-09-14 13:09 ` Will Deacon
2020-09-03 9:17 ` [PATCH v2 03/10] kvm: arm64: Remove __hyp_this_cpu_read David Brazdil
2020-09-10 11:12 ` Andrew Scull
2020-09-17 8:34 ` David Brazdil
2020-09-03 9:17 ` [PATCH v2 04/10] kvm: arm64: Remove hyp_adr/ldr_this_cpu David Brazdil
2020-09-10 12:34 ` Andrew Scull
2020-09-03 9:17 ` [PATCH v2 05/10] kvm: arm64: Add helpers for accessing nVHE hyp per-cpu vars David Brazdil
2020-09-03 9:17 ` [PATCH v2 06/10] kvm: arm64: Duplicate arm64_ssbd_callback_required for nVHE hyp David Brazdil
2020-09-03 9:17 ` [PATCH v2 07/10] kvm: arm64: Create separate instances of kvm_host_data for VHE/nVHE David Brazdil
2020-09-03 9:17 ` [PATCH v2 08/10] kvm: arm64: Mark hyp stack pages reserved David Brazdil
2020-09-03 9:17 ` [PATCH v2 09/10] kvm: arm64: Set up hyp percpu data for nVHE David Brazdil
2020-09-03 9:17 ` [PATCH v2 10/10] kvm: arm64: Remove unnecessary hyp mappings David Brazdil
2020-09-10 14:07 ` Andrew Scull
2020-09-16 13:35 ` David Brazdil
2020-09-14 17:40 ` [PATCH v2 00/10] Independent per-CPU data section for nVHE Will Deacon
2020-09-16 11:54 ` David Brazdil [this message]
2020-09-16 12:24 ` David Brazdil
2020-09-16 12:39 ` Will Deacon
2020-09-16 12:40 ` David Brazdil
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