[Part1 PATCH v7 15/17] percpu: Introduce DEFINE_PER_CPU_DECRYPTED

From: Brijesh Singh
Date: Fri Oct 20 2017 - 10:32:46 EST


KVM guest defines three per-CPU variables (steal-time, apf_reason, and
avic_eio) 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@xxxxxxx>
Acked-by: Tejun Heo <tj@xxxxxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Tested-by: Borislav Petkov <bp@xxxxxxx>
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>
---
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 353f52fdc35e..bdcd1caae092 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -779,6 +779,24 @@
#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
@@ -816,6 +834,7 @@
. = 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 8f16299ca068..2d2096ba1cfe 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__.
--
2.9.5