arm64: VHE: Add support for running Linux in EL2 mode

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.

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 8cc62289a63ed9958c9623acaa5462048cc9287b..cf118d93290da323fbaca4e1d89fdbd19967ddcf 100644 (file)
--- 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 917d98108b3f05d9b1013020f9f576a3db776bc6..6f2f37743d3b34994b9d91fb1f99890910accbad 100644 (file)
--- 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