[Part1 PATCH v4 15/17] percpu: introduce DEFINE_PER_CPU_UNENCRYPTED

[Brijesh Singh]

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

DEFINE_PER_CPU_UNENCRYPTED can be used to define the per-cpu variables
which will be shared between guest and hypervisor. Currently, KVM defines
three variables (steal-time, apf_reason, and avic_eio) which are shared
with hypervisor.

Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: Arnd Bergmann <arnd@xxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: linux-arch@xxxxxxxxxxxxxxx
Cc: x86@xxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
---
 include/asm-generic/vmlinux.lds.h | 11 +++++++++++
 include/linux/percpu-defs.h       | 15 +++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 8acfc1e099e1..363858f43cbc 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -777,6 +777,16 @@
 #define INIT_RAM_FS
 #endif
 
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+#define PERCPU_UNENCRYPTED_SECTION					\
+	. = ALIGN(PAGE_SIZE);						\
+	*(.data..percpu..unencrypted)					\
+	. = ALIGN(PAGE_SIZE);
+#else
+#define PERCPU_UNENCRYPTED_SECTION
+#endif
+
+
 /*
  * Default discarded sections.
  *
@@ -815,6 +825,7 @@
 	. = ALIGN(cacheline);						\
 	*(.data..percpu)						\
 	*(.data..percpu..shared_aligned)				\
+	PERCPU_UNENCRYPTED_SECTION					\
 	VMLINUX_SYMBOL(__per_cpu_end) = .;
 
 /**
diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
index 8f16299ca068..b2b99ad4b31d 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 unencrypted when memory encryption is enabled in the guest.
+ */
+#if defined(CONFIG_VIRTUALIZATION) && defined(CONFIG_AMD_MEM_ENCRYPT)
+
+#define DECLARE_PER_CPU_UNENCRYPTED(type, name)				\
+	DECLARE_PER_CPU_SECTION(type, name, "..unencrypted")
+
+#define DEFINE_PER_CPU_UNENCRYPTED(type, name)				\
+	DEFINE_PER_CPU_SECTION(type, name, "..unencrypted")
+#else
+#define DEFINE_PER_CPU_UNENCRYPTED(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__.
-- 
2.9.5