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@amd.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Borislav Petkov <bp@suse.de>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: linux-arch@vger.kernel.org
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: kvm@vger.kernel.org
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christoph Lameter <cl@linux.com>
Link: https://lkml.kernel.org/r/20171020143059.3291-16-brijesh.singh@amd.com
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) = .;
/**