[PATCH v3 22/23] arm64: VHE: Add support for running Linux in EL2 mode

Marc Zyngier
2016-02-03T18:00:15Z

With ARMv8.1 VHE, the architecture is able to (almost) transparently
run the kernel at EL2, despite being written for EL1.

This patch takes care of the "almost" part, mostly preventing the kernel
from dropping from EL2 to EL1, and setting up the HYP configuration.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm64/Kconfig | 13 +++++++++++++
arch/arm64/kernel/head.S | 28 +++++++++++++++++++++++++++-
2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 8cc6228..cf118d9 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -750,6 +750,19 @@ config ARM64_LSE_ATOMICS
not support these instructions and requires the kernel to be
built with binutils >= 2.25.

+config ARM64_VHE
+ bool "Enable support for Virtualization Host Extensions (VHE)"
+ default y
+ help
+ Virtualization Host Extensions (VHE) allow the kernel to run
+ directly at EL2 (instead of EL1) on processors that support
+ it. This leads to better performance for KVM, as they reduce
+ the cost of the world switch.
+
+ Selecting this option allows the VHE feature to be detected
+ at runtime, and does not affect processors that do not
+ implement this feature.
+
endmenu

endmenu
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 917d981..6f2f377 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -30,6 +30,7 @@
#include <asm/cache.h>
#include <asm/cputype.h>
#include <asm/kernel-pgtable.h>
+#include <asm/kvm_arm.h>
#include <asm/memory.h>
#include <asm/pgtable-hwdef.h>
#include <asm/pgtable.h>
@@ -464,9 +465,27 @@ CPU_LE( bic x0, x0, #(3 << 24) ) // Clear the EE and E0E bits for EL1
isb
ret

+2:
+#ifdef CONFIG_ARM64_VHE
+ /*
+ * Check for VHE being present. For the rest of the EL2 setup,
+ * x2 being non-zero indicates that we do have VHE, and that the
+ * kernel is intended to run at EL2.
+ */
+ mrs x2, id_aa64mmfr1_el1
+ ubfx x2, x2, #8, #4
+#else
+ mov x2, xzr
+#endif
+
/* Hyp configuration. */
-2: mov x0, #(1 << 31) // 64-bit EL1
+ mov x0, #HCR_RW // 64-bit EL1
+ cbz x2, set_hcr
+ orr x0, x0, #HCR_TGE // Enable Host Extensions
+ orr x0, x0, #HCR_E2H
+set_hcr:
msr hcr_el2, x0
+ isb

/* Generic timers. */
mrs x0, cnthctl_el2
@@ -526,6 +545,13 @@ CPU_LE( movk x0, #0x30d0, lsl #16 ) // Clear EE and E0E on LE systems
/* Stage-2 translation */
msr vttbr_el2, xzr

+ cbz x2, install_el2_stub
+
+ mov w20, #BOOT_CPU_MODE_EL2 // This CPU booted in EL2
+ isb
+ ret
+
+install_el2_stub:
/* Hypervisor stub */
adrp x0, __hyp_stub_vectors
add x0, x0, #:lo12:__hyp_stub_vectors
--
2.1.4