linux-kernel - Re: [PATCH v2 00/10] Independent per-CPU data section for nVHE

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Message-ID: <20200916122412.elxfxbdygvmdgrj5@google.com>
Date:   Wed, 16 Sep 2020 13:24:12 +0100
From:   David Brazdil <dbrazdil@...gle.com>
To:     Will Deacon <will@...nel.org>
Cc:     Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Arnd Bergmann <arnd@...db.de>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, linux-arch@...r.kernel.org,
        kernel-team@...roid.com
Subject: Re: [PATCH v2 00/10] Independent per-CPU data section for nVHE

> 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. 

Seems to work. Can't use PERCPU_SECTION directly because then we couldn't
rename it in the same linker script, but if we just unwrap that one layer
we can use PERCPU_INPUT. No global macro changes needed.

Let me know what you think.

------8<------
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 5904a4de9f40..9e6bf21268f1 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -195,11 +195,9 @@ SECTIONS
        PERCPU_SECTION(L1_CACHE_BYTES)

        /* KVM nVHE per-cpu section */
-       #undef PERCPU_SECTION_NAME
-       #undef PERCPU_SYMBOL_NAME
-       #define PERCPU_SECTION_NAME(suffix)     CONCAT3(.hyp, PERCPU_SECTION_BASE_NAME, suffix)
-       #define PERCPU_SYMBOL_NAME(name)        __kvm_nvhe_ ## name
-       PERCPU_SECTION(L1_CACHE_BYTES)
+       . = ALIGN(PAGE_SIZE);
+       .hyp.data..percpu : { *(.hyp.data..percpu) }
+       . = ALIGN(PAGE_SIZE);

        .rela.dyn : ALIGN(8) {
                *(.rela .rela*)
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
index 7d8c3fa004f4..1d8e4f7edc29 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
@@ -4,6 +4,10 @@
  * Written by David Brazdil <dbrazdil@...gle.com>
  */

+#include <asm-generic/vmlinux.lds.h>
+#include <asm/cache.h>
+#include <asm/memory.h>
+
 /*
  * Defines an ELF hyp section from input section @NAME and its subsections.
  */
@@ -11,9 +15,9 @@

 SECTIONS {
        HYP_SECTION(.text)
-       HYP_SECTION(.data..percpu)
-       HYP_SECTION(.data..percpu..first)
-       HYP_SECTION(.data..percpu..page_aligned)
-       HYP_SECTION(.data..percpu..read_mostly)
-       HYP_SECTION(.data..percpu..shared_aligned)
+
+       .hyp..data..percpu : {
+               __per_cpu_load = .;
+               PERCPU_INPUT(L1_CACHE_BYTES)
+       }
 }
-----8<------

David