[PATCH] kvm: arm64: correctly align nVHE percpu data

From: Jamie Iles <jamie@nuviainc.com>
To: linux-arm-kernel@lists.infradead.org
Cc: Marc Zyngier <maz@kernel.org>, Jamie Iles <jamie@nuviainc.com>,
	David Brazdil <dbrazdil@google.com>,
	Will Deacon <will@kernel.org>
Subject: [PATCH] kvm: arm64: correctly align nVHE percpu data
Date: Fri, 13 Nov 2020 15:04:06 +0000	[thread overview]
Message-ID: <20201113150406.14314-1-jamie@nuviainc.com> (raw)
In-Reply-To: <20201113101227.zb6ckyriobjrlkc5@google.com>

The nVHE percpu data is partially linked but the nVHE linker script did
not align the percpu section.  The PERCPU_INPUT macro would then align
the data to a page boundary:

  #define PERCPU_INPUT(cacheline)					\
  	__per_cpu_start = .;						\
  	*(.data..percpu..first)						\
  	. = ALIGN(PAGE_SIZE);						\
  	*(.data..percpu..page_aligned)					\
  	. = ALIGN(cacheline);						\
  	*(.data..percpu..read_mostly)					\
  	. = ALIGN(cacheline);						\
  	*(.data..percpu)						\
  	*(.data..percpu..shared_aligned)				\
  	PERCPU_DECRYPTED_SECTION					\
  	__per_cpu_end = .;

but then when the final vmlinux linking happens the hypervisor percpu
data is included after page alignment and so the offsets potentially
don't match.  On my build I saw that the .hyp.data..percpu section was
at address 0x20 and then the percpu data would begin at 0x1000 (because
of the page alignment in PERCPU_INPUT), but when linked into vmlinux,
everything would be shifted down by 0x20 bytes.

This manifests as one of the CPUs getting lost when running
kvm-unit-tests or starting any VM and subsequent soft lockup on a Cortex
A72 device.

Fixes: 30c953911c43 ("kvm: arm64: Set up hyp percpu data for nVHE")
Cc: David Brazdil <dbrazdil@google.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Jamie Iles <jamie@nuviainc.com>
---
v2: add clarifying commentary

 arch/arm64/kvm/hyp/nvhe/hyp.lds.S | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
index bb2d986ff696..a797abace13f 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
+++ b/arch/arm64/kvm/hyp/nvhe/hyp.lds.S
@@ -13,6 +13,11 @@
 
 SECTIONS {
 	HYP_SECTION(.text)
+	/*
+	 * .hyp..data..percpu needs to be page aligned to maintain the same
+	 * alignment for when linking into vmlinux.
+	 */
+	. = ALIGN(PAGE_SIZE);
 	HYP_SECTION_NAME(.data..percpu) : {
 		PERCPU_INPUT(L1_CACHE_BYTES)
 	}
-- 
2.27.0


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