linux-kernel - [tip:x86/asm] percpu: Introduce DEFINE_PER_CPU

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Date:   Tue, 7 Nov 2017 06:48:41 -0800
From:   tip-bot for Brijesh Singh <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     bp@...en8.de, tj@...nel.org, hpa@...or.com, cl@...ux.com,
        tglx@...utronix.de, thomas.lendacky@....com, mingo@...nel.org,
        linux-kernel@...r.kernel.org, arnd@...db.de, brijesh.singh@....com,
        bp@...e.de
Subject: [tip:x86/asm] percpu: Introduce DEFINE_PER_CPU_DECRYPTED

Commit-ID:  ac26963a1175c813e3ed21c0d2435b083173136e
Gitweb:     https://git.kernel.org/tip/ac26963a1175c813e3ed21c0d2435b083173136e
Author:     Brijesh Singh <brijesh.singh@....com>
AuthorDate: Fri, 20 Oct 2017 09:30:57 -0500
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Tue, 7 Nov 2017 15:35:59 +0100

percpu: Introduce DEFINE_PER_CPU_DECRYPTED

KVM guest defines three per-CPU variables (steal-time, apf_reason, and
kvm_pic_eoi) which are shared between a guest and a hypervisor.

When SEV is active, memory is encrypted with a guest-specific key, and if
the guest OS wants to share the memory region with the hypervisor then it
must clear the C-bit (i.e set decrypted) before sharing it.

DEFINE_PER_CPU_DECRYPTED can be used to define the per-CPU variables
which will be shared between a guest and a hypervisor.

Signed-off-by: Brijesh Singh <brijesh.singh@....com>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Tested-by: Borislav Petkov <bp@...e.de>
Acked-by: Tejun Heo <tj@...nel.org>
Reviewed-by: Borislav Petkov <bp@...e.de>
Cc: linux-arch@...r.kernel.org
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: kvm@...r.kernel.org
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Christoph Lameter <cl@...ux.com>
Link: https://lkml.kernel.org/r/20171020143059.3291-16-brijesh.singh@amd.com

---
 include/asm-generic/vmlinux.lds.h | 19 +++++++++++++++++++
 include/linux/percpu-defs.h       | 15 +++++++++++++++
 2 files changed, 34 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 63e56f6..c58f380 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -778,6 +778,24 @@
 #endif
 
 /*
+ * Memory encryption operates on a page basis. Since we need to clear
+ * the memory encryption mask for this section, it needs to be aligned
+ * on a page boundary and be a page-size multiple in length.
+ *
+ * Note: We use a separate section so that only this section gets
+ * decrypted to avoid exposing more than we wish.
+ */
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+#define PERCPU_DECRYPTED_SECTION					\
+	. = ALIGN(PAGE_SIZE);						\
+	*(.data..percpu..decrypted)					\
+	. = ALIGN(PAGE_SIZE);
+#else
+#define PERCPU_DECRYPTED_SECTION
+#endif
+
+
+/*
  * Default discarded sections.
  *
  * Some archs want to discard exit text/data at runtime rather than
@@ -815,6 +833,7 @@
 	. = ALIGN(cacheline);						\
 	*(.data..percpu)						\
 	*(.data..percpu..shared_aligned)				\
+	PERCPU_DECRYPTED_SECTION					\
 	VMLINUX_SYMBOL(__per_cpu_end) = .;
 
 /**
diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
index 8f16299..2d2096b 100644
--- a/include/linux/percpu-defs.h
+++ b/include/linux/percpu-defs.h
@@ -173,6 +173,21 @@
 	DEFINE_PER_CPU_SECTION(type, name, "..read_mostly")
 
 /*
+ * Declaration/definition used for per-CPU variables that should be accessed
+ * as decrypted when memory encryption is enabled in the guest.
+ */
+#if defined(CONFIG_VIRTUALIZATION) && defined(CONFIG_AMD_MEM_ENCRYPT)
+
+#define DECLARE_PER_CPU_DECRYPTED(type, name)				\
+	DECLARE_PER_CPU_SECTION(type, name, "..decrypted")
+
+#define DEFINE_PER_CPU_DECRYPTED(type, name)				\
+	DEFINE_PER_CPU_SECTION(type, name, "..decrypted")
+#else
+#define DEFINE_PER_CPU_DECRYPTED(type, name)	DEFINE_PER_CPU(type, name)
+#endif
+
+/*
  * Intermodule exports for per-CPU variables.  sparse forgets about
  * address space across EXPORT_SYMBOL(), change EXPORT_SYMBOL() to
  * noop if __CHECKER__.